A powerful tsunami triggered by a massive earthquake devastated the northeastern coast of Japan on Friday, leaving hundreds dead and launching waves that triggered warnings from Alaska to South America.

The Japan Meteorological Agency said the 8.9-magnitude earthquake was the strongest in the country’s history. Television footage showed towering waves surging toward the northeastern shoreline, pulling cars into the water and knocking boats and buildings onto their sides.

Initial forecasts warned of potential devastation throughout the Pacific Rim, including Hawaii, and reaching east around the globe to the continental United States. But the waves that reached Hawaii about 8 a.m. Washington time were relatively modest, and officials said the tsunami would have minimal impact on the West Coast.

Japan’s Kyodo News agency said between 200 and 300 bodies were found near Sendai, the capital of Miyagi Prefecture and the population center nearest the epicenter of the quake.

The agency later reported that the death toll was likely to surpass 1,000.

Early Saturday, a 6.6 magnitude earthquake on a different fault line in central Japan caused buildings to sway in Tokyo, the Associated Press reported. The U.S. Geological Survey recorded two quakes Saturday near the west coast of Honshu, Japan’s main island. It said a 6.2 magnitude quake about 121 miles northwest of Tokyo was followed less than an hour later by a 6.6 temblor 331 miles north of the capital.

In Washington, President Obama said he was “heartbroken” by the tragedy and offered “whatever assistance is needed.”

Speaking about 12 hours after the quake struck, Obama said the United States has not suffered “any major damage so far” from the resulting tsunami. But waves that struck northern California near the Oregon border later swept four people out to sea, damaged three dozen boats and wrecked the harbor of Crescent City, Calif. One of the four victims — a man who was pulled out to sea while photographing the tsunami — was missing and feared dead, and the Coast Guard was searching for him, news services reported.

Damage was also reported to fishing boats and wooden docks in Santa Cruz on the central California coast.

Although thousands of people fled their homes along the California coast, scientists said the main thrust of the tsunami was to the southeast, across the Pacific toward South America. As a result, Chile upgraded a tsunami alert Friday and braced for impact later in the day.

In Japan, houses floated like rafts along the waves when the tsunami hit. In some areas, the wall of water looked more like a black shroud of sludge and debris, consuming a vast, flat patchwork of farmland. About eight hours after the quake, officials told the news service that they had lost contact with at least one train traveling in that area, and a ship carrying at least 100 people was said to have been swept out to sea.

The national police agency confirmed 137 deaths, news services reported, with officials saying that number was sure to rise as emergency workers gained access to the hardest-hit areas.

According to the U.S. Geological Survey, an 8.9-magnitude quake would be the fifth-largest earthquake in recorded history (see a list of the largest quakes since 1900). It was significantly more powerful than the 7.0-magnitude earthquake that struck Haiti in January 2010, killing more than 300,000. The earthquake that struck Christchurch, New Zealand, last month had a magnitude of 6.3.

The survey said the powerful quake was followed over the next 10 hours by at least 79 aftershocks in the region, 16 of them greater than 6.0 magnitude. One of them, 39 minutes after the main quake, was recorded at 7.1 magnitude, greater than the Haiti earthquake.

In recent days, Japan had experienced a series of smaller tremors.

Prime Minister Naoto Kan addressed the nation shortly after the quake, saying the government will do “everything possible to minimize the damage” and calling for international assistance. “We ask the people of Japan to exercise the spirit of fraternity and act fast and to assist one’s family and neighbors,” Kan said.

Japan’s stock market closed down 1.7 percent, and global markets fell sharply as well.

Obama said he spoke to Kan and offered U.S. help. He told reporters that the main way the United States could assist would be in providing “lift capacity” to help in the cleanup. “You have huge disruptions,” he said, with “boats and houses and cars that are washed into the main thoroughfares, and that requires heavy equipment.”

“I am heartbroken by this tragedy,” Obama said. He said it reminded him that “for all our differences . . . ultimately humanity is one.” He cited his “close personal connection” with Japanese culture from having grown up in Hawaii, which he said “makes our concerns that much more acute.” But he expressed confidence that Japan, relying on its people’s resourcefulness and its economic might, “will successfully rebuild.”

Obama was briefed on the quake about 4 a.m. Eastern time. Several countries, including Russia and South Korea, put emergency crews on standby.

The U.S. military redeployed several ships toward Japan on Friday and began preparing for humanitarian-relief missions in the expectation that it would be asked to help respond to the disaster.

U.S. Air Force planes in Japan, meanwhile, delivered coolant to a nuclear power plant affected by the quake, Secretary of State Hillary Rodham Clinton said.

“They have very high engineering standards, but one of their plants came under a lot of stress with the earthquake and didn’t have enough coolant, and so Air Force planes were able to deliver that,” she said.

Obama told reporters that he asked Kan about the vulnerability of Japan’s nuclear power plants in their phone conversation and was told that “so far they have not seen evidence of radiation leaks.” Nevertheless, Obama said, “obviously you’ve got to take all precautions.”

About 70 search-and-rescue teams have been put on standby around the world awaiting a Japanese government request for assistance in digging out survivors, according to Nicholas Reader, a spokesman for the U.N. Office for the Coordination of Humanitarian Affairs.

In Virginia, the Fairfax County Fire and Rescue Department was assembling a 72-member search-and-rescue team Friday in anticipation of an order to fly to Japan to help find survivors. The team, which also includes paramedics, doctors, engineers and others, was mobilized by the U.S. Agency for International Development but was still awaiting a final deployment order.

The quake struck at 2:46 p.m. local time (12:46 a.m. in Washington) at a depth of 15 miles and about 80 miles off the coast of Miyagi Prefecture, a mostly rural but still densely populated part of Honshu, Japan’s largest island.

Tokyo — which is also on Honshu and about 230 miles south of the epicenter — appeared to escape substantial damage, although some fires were reported and buildings shook violently for several minutes during the initial quake.

At least 2 million people were without power in the capital. Rail service was temporarily halted. Mobile phone communication — a staple in Japan — was largely disrupted. Narita International Airport, the main international gateway, canceled all its flights for the afternoon and evening but resumed outgoing flights late Friday night.

Workers and residents fled from buildings, terrified by the aftershocks that continued for hours and refusing to return indoors. With the normally reliable mass transit system shut down, thousands of commuters from Tokyo’s expansive suburbs were stranded, unable to find a taxi. Shelters opened their doors to accommodate them; some spent the night in temples, university buildings and concert halls.

Japan’s government urged thousands to evacuate from the area around Fukushima No. 1 power plant, a nuclear power station 170 miles northeast of Tokyo, after its cooling system failed.

The malfunction did not result in the leak of any radioactive material, a government spokesman said, and the plant — like all Japan’s nuclear facilities — automatically shut down after the earthquake.

But power outages, and the subsequent failure of backup generators necessary for the cooling process, prompted officials to order the evacuation. Late Friday, a government spokesman said the situation at the plant was under control. Kyodo also reported an explosion at a petrochemical plant in Sendai.

The destruction will strain the resources of a country already struggling with a two-decade economic stagnation and a burdensome public debt.

“Our initial assessment indicates that there has already been enormous damage,” said Yukio Edano, the government’s top spokesman. “We will make maximum relief effort based on that assessment.”

As one of the world’s most earthquake-susceptible countries, Japan has invested significant resources in guarding itself. A strict building code enacted in 1981 requires structures to be built using ductile reinforced concrete, which provides flexibility that can help withstand significant tremors.

The 1995 Kobe earthquake — until Friday the country’s most devastating — leveled many buildings built before the 1981 code was in place. The death toll from that earthquake, which struck a much more heavily populated area, rose above 6,000.

Since Kobe, many public buildings have been reinforced. Every year, Japan also conducts disaster-preparedness exercises.

The country has also fortified coastal cities against quake-triggered tsunamis — building a system of flood gates in Tokyo, for example, to divert the walls of water that a major quake can generate. But live television footage showed dramatic devastation well north of the capital, as water first receded and then crashed forward, moving faster than anybody who tried to outrun or out-drive it.

On land, there were reports of fallen buildings and people buried beneath them. In Sendai, the airport was underwater, and employees and passengers crowded on the building’s roof. Flooding dislodged the foundations of buildings, even as fires consumed them from the top.

In industrial Chiba Prefecture, just east of Tokyo, a fire blazed at an oil refinery.

In the hours after the quake, authorities ordered evacuations from low-lying areas on the U.S. island territory of Guam in the western Pacific, but the tsunami did not wreak havoc there, according to news reports.

Tsunami warnings or alerts were issued for dozens of places around the globe, including the West Coast of the United States, Hawaii and Alaska. The Pacific Tsunami Warning Center said a tsunami struck Hawaii about 3 a.m. (8 a.m. in Washington) but caused little damage.

Russian authorities on the Kuril Islands, northeast of Japan, evacuated more than 11,000 residents from coastal areas as waves as high as 10 feet hit the shore, according to Russia’s Emergencies Ministry. Aftershocks measured at a magnitude of 5.0 were felt on the islands, but no deaths or serious destruction were reported.

A tsunami generated by the quake began reaching the coast of Washington state and Oregon shortly after 7 a.m. Pacific time, bringing waves of more than eight feet in amplitude in some places, according to the West Coast and Alaska Tsunami Warning Center. Amplitude is a measurement relative to normal sea level that amounts to roughly half the wave height from crest to trough.

“Tsunami amplitudes are expected to peak two to three hours after initial arrival along the North American coast,” the center warned. It said wave heights are amplified by irregular shoreline and can be difficult to forecast. While mariners in water deeper than 600 feet should not be affected by a tsunami, the center said, wave heights increase rapidly as the water becomes more shallow, resulting in a series of waves that can be dangerous for several hours after the initial impact.

The greatest wave amplitude forecast by the center (8.5 feet) was at Oregon’s Siletz Bay, the site of a national wildlife refuge. California’s Point San Luis near San Luis Obispo was forecast to get a wave of seven feet in amplitude.

In Washington, military officials said Navy ships are responding to the disaster in Japan.

The USS Tortuga, a dock-landing ship homeported in Sasebo, southern Japan, was expected to head north Friday to parts of the country most seriously affected by the quake, said Col. David Lapan, a Defense Department spokesman.

The USS Blue Ridge, the command ship of the Navy’s 7th Fleet, was loading humanitarian assistance supplies in Singapore in preparation to sail to northern Japan, he said.

The USS Essex, an amphibious warfare ship that resembles a small aircraft carrier, was readying to leave for Japan from Malaysia, where it had just arrived for a port call early Friday. The Essex also carries Marines from the 31st Marine Expeditionary Unit.

The USS Ronald Reagan, an aircraft carrier, and its strike group were in the western Pacific near the Korean Peninsula but were turning toward Japan in case they are needed as well, Lapan said.

Among other capabilities, the U.S. ships could provide airlift and rescue support, as well as deliver food, water and medical supplies.

The Defense Department has about 38,000 military personnel based in Japan, as well as 5,000 U.S. civilian employees and 43,000 family members. Lapan said there were no reports of any deaths of U.S. service members or their dependents from the tsunami, nor any reports of serious damage to U.S. military assets or installations.

He said Yokota Air Base, a U.S. military installation near Tokyo, had allowed more than 10 commercial airliners to land after they were diverted from Tokyo’s Narita International Airport. Among the airliners that diverted flights to Yokota were Delta, United and KLM.

The closest U.S. military installation to the quake’s epicenter is Misawa Air Base, about 400 miles north of Tokyo.

Staff writers William Branigin, Debbi Wilgoren, Craig Whitlock and Mary Beth Sheridan in Washington and correspondent Kathy Lally in Moscow contributed to this report.