Vasily V. Titov, director of the National Oceanic and Atmospheric Administration’s Center for Tsunami Research, said that coastal areas closest to the center of the earthquake probably had about 15 to 30 minutes before the first wave of the tsunami struck. “In Japan, the public is among the best educated in the world about earthquakes and tsunamis,” he said. “But it’s still not enough time.”

Complicating the issue, he added, is that the flat terrain in the area would have made it difficult for people to reach higher, and thus safer, ground. On Friday, NHK television showed images of a huge fire sweeping across Kesennuma, a city of more than 70,000 people in the northeast. Whole blocks appeared to be ablaze. NHK also showed aerial images of columns of flame rising from an oil refinery and flood waters engulfing the Sendai airport, where survivors clustered on the roof. The runway was partly submerged. The refinery fire sent a plume of thick black smoke from blazing spherical storage tanks.

Even in Tokyo, far from the epicenter, the quake struck hard. William M. Tsutsui, a professor of Japanese business and economic history at Southern Methodist University in Dallas, was traveling in Tokyo with a business delegation when the ground began to shake. “What was scariest was to look up at the skyscrapers all around,” he said. “They were swaying like trees in the breeze.”

Prime Minister Naoto Kan said the quake and tsunami caused major damage across wide areas.

The United States Geological Survey said the quake was the most severe worldwide since an 8.8-magnitude quake off the coast of Chile a little more than a year ago that killed more than 400. It was less powerful than the 9.1-magnitude quake that struck off Northern Sumatra in late 2004. That quake set off a tsunami that killed more than 200,000 people around the Indian Ocean.