Police said 200 to 300 bodies have been found in the northeastern coastal city of Sendai. Police said another 88 were confirmed killed and 349 were missing.
The death toll was likely to continue climbing given the scale of the disaster.
The magnitude 8.9 offshore quake unleashed a 23-foot (7-meter) tsunami and was followed by more than 50 aftershocks for hours, many of them of more than magnitude 6.0.
The government ordered thousands of residents near a nuclear power plant in Onahama city to evacuate because the plant's system was unable to cool the reactor. The reactor was not leaking radiation but its core remained hot even after a shutdown. The plant is 170 miles (270 kilometers) northeast of Tokyo.
Dozens of cities and villages along a 1,300-mile (2,100-kilometer) stretch of coastline were shaken by violent tremors that reached as far away as Tokyo, hundreds of miles (kilometers) from the epicenter.
"The earthquake has caused major damage in broad areas in northern Japan," Prime Minister Naoto Kan said at a news conference.