A powerful earthquake rocked Taiwan early today, killing more than 600 people and injuring thousands as buildings collapsed in Taipei, the capital, and other cities and towns across the island.

The epicenter of the quake, which the U.S. Geological Survey measured at 7.6 on the Richter scale, was near the central Taiwan county of Nantou, about 90 miles south-southwest of Taipei.

Buildings were damaged in at least 19 cities and counties, according to Taiwan's Interior Ministry, which is overseeing disaster relief operations. The hardest-hit areas included Nantou, where at least 335 people were confirmed killed, and nearby Taichung county, where there were at least 249 fatalities, Taiwanese officials said.

In the town of Puli, a key government office building crashed to the ground, an Interior Ministry official said in a telephone interview. Local radio reports said a rice wine factory near the epicenter exploded and dozens of other buildings in the area were soundly shaken.

"We're trying to dig people out from underneath buildings," another Interior Ministry official said.

The earthquake, the strongest to hit the island since 1935, struck at 1:47 a.m. (1:47 p.m. EDT) as most of Taiwan's 22 million people were asleep. Taiwan television showed footage of injured residents milling outside mangled buildings in their underwear and pajamas. Power was out in wide swaths of northern Taiwan, including the capital.

In the aftermath of the quake, the U.S. Geological Survey's National Earthquake Information Center issued warnings of possible tsunamis, or powerful seismic sea waves, for Taiwan, Japan and the Philippines, in addition to the islands of Yap, Guam and Palau. The alerts were later canceled.

In Taipei, the 12-story Sungshan Hotel collapsed, and rescue workers were searching for more than 100 people believed to be trapped inside, according to the Associated Press. "Hurry. Go rescue people. They're in there. They're inside," said one unidentified woman who had been rescued from the hotel. "I lived on the ninth floor, but now it's the fourth floor."

In the Chang Hua district of central Taiwan, a row of houses collapsed, injuring at least three people and trapping at least 10 others, state-run radio reported.

As of noon, the Interior Ministry's disaster management center said 656 people were confirmed dead and about 3,000 injured. At least 1,245 people were reported trapped under the rubble.

An Interior Ministry official said he expected the toll to climb because some places were reporting figures more slowly than others.

Several countries, including the United States, were dispatching search and rescue teams. Seventy specialists from Fairfax County were leaving for Taiwan early Tuesday, said Capt. Mike Reilly, spokesman for the county, while an advance team of about 14 people from Fairfax as well as Miami-Dade County, Fla., and the federal Agency for International Development, was departing separately, officials said. The advance team includes cave-in, safety and logistics specialists.

Many of the Fairfax personnel just recently returned from Turkey, where they helped recovery efforts in the aftermath of that country's devastating earthquake.

Taiwan is situated in a region of dynamic seismic activity, and the island's residents have become somewhat accustomed to earthquakes, most of them small. But today's quake was the most violent in years, and it was followed by numerous aftershocks.

President Lee Teng-hui urged people to stay calm and reassured the public that the government has mobilized all its resources to handle the disaster, the Reuters news agency reported. Stock and currency markets, in addition to schools and offices in Taipei, were ordered closed today.

Idaho Gov. Dirk Kempthorne (R), who is visiting Taipei as part of a trade mission, told the Associated Press that he was sleeping in a top-floor room at the 25-story Grant Hyatt Regency Hotel in Taipei when the earthquake shook him awake.

"I think many of us thought we might be done for," he said. "It increased in intensity until you were virtually thrown from the bed."

A spokesman at the U.S. Geological Survey noted that the breadth of of the quake was about the same as that of the recent deadly temblor that killed more than 15,000 people in northwestern Turkey. "This is similar," Stuart Koyanagi told CNN, "but we still don't know how deep below the surface the earthquake was.

"We estimate this is a major earthquake," he said. "We only record five to 10 such quakes a year."