TOKYO (AFP) - A strong 6.3-magnitude earthquake struck off Japan's southern Kyushu island on Friday, the US Geological Survey (USGS) reported, but no tsunami warning was issued.

The epicentre of the quake - which struck at 2:06 am (1706 GMT Thursday) - was located 13 kilometres (eight miles) north of the city of Kunisaki-shi, USGS said.

The quake hit at a depth of 82 kilometres.

There was no tsunami alert issued, Japan's Meteorological Agency said as cited by Kyodo News, nor any immediate news of fatalities or damage.

Local authorities reported some minor injuries as people sought refuge following the quake, Kyodo said.

The quake, which the Japanese meteorological agency measured as having a preliminary magnitude of 6.1, registered a strong intensity in parts of Japan's Shikoku, Honshu and Kyushu islands, Kyodo reported.

There were no abnormalities detected at Ikata nuclear plant in Ehime prefecture or at Shimane plant in Shimane prefecture, the news agency said.

More than 18,000 people died when a 9.0-magnitude undersea earthquake sent a towering tsunami barrelling into Japan's northeast coast in March 2011 in the country's worst post-World War II disaster.

Cooling systems at the Fukushima nuclear plant were knocked out, sending reactors into meltdown and forcing tens of thousands of people to flee.