TOKYO (AFP) - A 6.4-magnitude earthquake struck off the east coast of Japan early Monday (April 20), according to the US Geological Survey (USGS), but no tsunami warning was issued.

The epicentre of the earthquake was 41.7km beneath the Pacific seabed, less than 50km off the coast of Miyagi prefecture, the USGS said on its website, rating the risk of casualties and damage as low.

The Japan Meteorological Agency (JMA) put the quake at a magnitude of 6.1 and a depth of 50km.

Japan's Kyodo News Agency said no tsunami warning had been issued after the tremor, which hit just after 5.30 am (2030 GMT).

Japan sits on the Pacific "Ring of Fire", an arc of intense seismic activity that stretches through Southeast Asia and across the Pacific basin.

In 2011, a devastating 9.0 magnitude earthquake struck roughly 130km east of Miyagi prefecture, unleashing an enormous tsunami, triggering the Fukushima nuclear reactor meltdown and killing nearly 16,000 people.