There were no immediate reports of damage or casualties and no widespread tsunami warning, although the initial earthquake was followed by five more quakes of magnitude five or above, one of them measuring 6.2.

The United States Geological Survey (USGS) said the first, 36.2-kilometre (22.6-mile) deep quake hit 108 kilometres east-south-east of the coastal town of Hachinohe, 574 kilometres from Tokyo, at 4:26 am (1926 GMT Friday).

The Pacific Tsunami Warning Center said that "no destructive widespread tsunami risk exists based on historical earthquake and tsunami data".

But it said that quakes of this size sometimes generate local tsunamis. "Authorities in the region of the epicentre should be aware of this," the centre said in a statement.

The Japan Meteorological Agency said that there might be some changes in sea levels due to the first earthquake, but that there were no reports of damage or casualties and none was expected, according to the Kyodo news agency.

It said the initial quake jolted Iwate prefecture, an area badly hit by the 9.0-magnitude earthquake and tsunami on March 11 that left almost 20,000 dead or missing and sparked the worst nuclear crisis since Chernobyl.

AFP