The magnitude 8.9 offshore quake unleashed a 23-foot (7-meter) tsunami and was followed by more than 20 aftershocks for hours, most of them of more than magnitude 6.0.
Police said at least 60 people were killed and 56 were missing. The death toll was likely to continue climbing given the scale of the disaster.
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.
Japan issued a state of emergency at a nuclear power plant after its cooling system had a mechanical failure. Trouble was reported at two other nuclear plants as well, but there was no radiation leak at any.
Chief Cabinet Secretary Yukio Edano said the measure at the nuclear power plant in Fukushima was a precaution and that the facility was not in immediate danger.
Even for a country used to earthquakes, this one was of horrific proportions because of the tsunami that crashed ashore, swallowing everything in its path as it surged several miles (kilometers) inland before retreating.
Large fishing boats and other sea vessels rode high waves into the cities, slamming against overpasses or scraping under them, snapping power lines along the way. Upturned and partially submerged vehicles were seen bobbing in the water. Ships anchored in ports crashed against each other.
