A strong 6.1 magnitude earthquake has rattled Japan's Ibaraki prefecture south of the stricken Fukushima No. 1 nuclear plant, the country's meteorological agency said, but no tsunami warning was issued.
The quake shook buildings in Tokyo, but no damage was immediately reported, public broadcaster NHK said, adding that flights at the capital's Narita Airport were temporarily suspended for safety checks.
Meanwhile, the number of people confirmed as dead or listed as missing by Japan's national police agency has topped 18,000, eight days after the massive earthquake and tsunami struck.
There were fears of a far higher death toll from the disaster that wiped out vast residential areas along the Pacific coast of northern Honshu island.
The national police agency said 7197 people had been confirmed dead and 10,905 officially listed as missing - a total of 18,102 - as of 9am today (1100 AEDT) as a result of the March 11 catastrophe.