This roundup of the state of the crisis in Japan following Friday's earthquake will be updated throughout the day.
How many deaths have resulted from the quake?
Early Monday morning (local time), authorities put the death toll at 1,597. That number could reach 10,000, reports Kyodo News. The police chief of Miyagi Prefecture said Sunday that there is "no question" that at least 10,000 in the prefecture of 2.3 million are dead.
How powerful was the quake?
The U.S. Geological survey has assigned the quake a magnitude of 8.9, while Japan's Meteorological Agency has upgraded it from an 8.8 to a 9.0. It is the most powerful earthquake to hit Japan since record-keeping began in the late 19th century. By comparison, the 2010 Haiti earthquake was a 7.0, and the 2010 Chile earthquake was an 8.8.
The Japanese television station NHK reports that there is a 70 percent chance of magnitude 7.0 aftershocks in the next three days.
Prime Minister Naoto Kan has called the disaster Japan's biggest crisis since World War II.
Which nuclear reactors are in danger?
The two plants that have been most affected so far are the Fukushima Daiichi (No. 1) and Fukushima Daini (No. 2) plants, both located in Fukushima Prefecture and run by the Tokyo Electric Power Company (TEPCO). The Fukushima Daiichi plant, the 14th-largest nuclear facility in the world, was the first to be severely damaged when an explosion Saturday crippled its unit 1 reactor and injured four workers, one of whom later died. The emergency cooling system at a second Daiichi reactor, unit 3, failed early Sunday, and engineers have injected seawater into both reactors to prevent overheating and avert a possible meltdown. However, because the water gauge at unit 3 is not working, it is impossible to tell whether the seawater maneuver has been effective. If the fuel rods in one of the reactors overheat to the point where they burn through the walls of the reactor, dangerous radiation would be released. An evacuation order has been issued for people within a 12-mile radius of the Daiichi plant and within 6 miles of the Daini plant.
Later on Sunday, a state of emergency was declared at a third nuclear plant, in Onagawa. Authorities say the three reactors in Onagawa are "under control."
How severe is the threat of a nuclear crisis in Japan?
Japan's nuclear safety agency has rated the damage to the Fukushima Daiichi plant a four out of seven on the International Nuclear and Radiological Event Scale. By comparison, the 1986 Chernobyl disaster was a seven, and the 1979 Three Mile Island meltdown was a five. A four signifies an "accident with local consequences."
What steps have been taken to aid victims of the quake?
Japan has deployed 100,000 soldiers in the rescue and recovery operation, doubling its initial deployment. The USS Ronald Reagan aircraft carrier, with its crew of almost 6,000, arrived in Japan on Saturday to assist Japanese troops; other U.S. warships are also providing assistance. Because of the difficulty of road travel, Japanese rescue forces have turned to efforts by sea and air, including helicopter rescues. Numerous international aid teams arrived in Japan on Sunday.
How hard has the tsunami hit the United States?
Tsunami waves hit the West Coast of the United States on Friday and smashed ships, ripped out docks and caused flooding in Hawaii, CNBC reported. At least five people along the West Coast were swept out to sea Friday, and one of them was missing and presumed dead. The sea level rose nearly three feet as far south as San Diego on Friday and destroyed the busiest recreation port on the Oregon coast. The cleanup effort is expected to cost millions of dollars.