The most powerful earthquake to hit Japan in at least 100 years unleashed walls of water Friday that swept across rice fields, engulfed towns, dragged houses onto highways and tossed cars and boats like toys, apparently killing hundreds and forcing the evacuations of tens of thousands.

Prime Minister Naoto Kan said the “enormously powerful” earthquake had caused “tremendous damage over a wide area.”

Japanese media, citing local and national police, said hundreds of people were dead and hundreds more missing. The 2:46 p.m. quake struck 373 kilometers (230 miles) from Tokyo, the United States Geological Survey said.

The quake prompted the U.S. National Weather Service to issue tsunami warnings for at least 50 countries and territories, although initial reports as the waves reached locations outside of Japan indicated no damage.

Japan’s Kyodo News Service, citing Japan’s defense forces, said 60,000 to 70,000 people were being evacuated to shelters in the Sendai area.

Japanese authorities ordered the precautionary evacuation of the area around a nuclear plant affected by the earthquake, saying that while there was no immediate danger, crews were having trouble cooling the reactor. The Fukushima plant is one of four closest to the quake that the U.N. nuclear watchdog agency said were safety shut down.

Video aired by NHK showed widespread fires in Hakodate in the southern part of Hokkaido island in northern Japan. An oil refinery was burning in Chiba Prefecture near Tokyo, according to NHK, and firefighters could not get close enough to fight it because of the heat. And Kyodo said fires could be seen in extensive areas of Kesennuma in Miyagi Prefecture.

President Barack Obama offered his condolences and said the United States is standing by to help “in this time of great trial.”

Images from Japanese media and CNN iReporters showed smoke pouring from buildings and water rushing across fields, carrying away entire structures.

“I wasn’t scared when it started … but it just kept going and going,” said Michelle Roberts, who lives in central Tokyo. “I won’t lie, it was quite scary. But we are all OK. We live on the third floor, so most everything shook and shifted.”