People living within a two-kilometre radius of the number two reactor of the Fukushima number one plant were advised to move away.
Firefighters have not yet been able to control a fire at another power station near Tokyo.
Earlier the government declared an atomic power emergency, but said no radiation leaks had been detected.
One of the country's high-speed bullet trains is reported to be missing.
The European Union meanwhile has announced it will mobilise "all appropriate assistance" for Japan.
More than 50 countries are on high alert for a tsunami. Russia, Australia and New Zealand have all been given the all clear.
World share prices dropped on the news of the earthquake and the yen sank to its lowest level for two and half weeks, before steadying.
The death toll has reached 60, with 244 injured and 56 reported missing.