Tsunami waves of up to 1 metre have hit the coast of north-eastern Japan after a powerful earthquake, the Meteorological Agency said on Saturday, dpa reported.
A magnitude-7.1 earthquake struck off the east coast of Japan's Fukushima region at 2:10 am (1710 GMT Friday), it said, adding that the damaged nuclear power plant there had not been affected.
The tremor's epicentre was located off Fukushima at a depth of 10 kilometres, the agency said. It had initially measured the earthquake at magnitude 6.8.
The US Geological Survey measured the quake at magnitude 7.3 in the Pacific Ocean about 300 kilometres from Fukushima's coast.
No abnormalities were detected at the damaged Fukushima Daiichi Nuclear Power Station, where three nuclear reactors suffered meltdowns after a tsunami swept through the plant in March 2011.
Radiation levels in a drainage channel at the nuclear plant more than doubled this week. The spike was probably caused after a recent heavy downpour washed radiation-contaminated soil into the ditch.