A 6.8-magnitude earthquake has struck off the coast of northeastern Japan, the US Geological Survey (USGS) has said, but authorities have not issued a tsunami warning and there were no immediate reports of damage.

The quake struck at 6:12am (21:12 GMT Tuesday) off the east coast of Japan's Honshu island in the Pacific Ocean at a depth of 38.9km, according to USGS.

Japan's meteorological agency said there was no immediate tsunami threat from the earthquake, which hit 33km southeast of the nearest city of Ofunato.

Large areas jolted by the latest tremor were among those damaged by the 2011 quake and tsunami that killed more than 18,000 people and triggered a nuclear meltdown at the Fukushima power plant.

Wednesday's earthquake did not damage any of the nuclear reactors in the region, including those at the crippled Fukushima facility, Japan's public broadcaster NHK said.

All of Japan's reactors have been off-line since the Fukushima disaster.

Train services in the region, including "Shinkansen" bullet train operations, were temporarily suspended following the quake, officials said.

Japan's islands are situated at the juncture of several tectonic plates and experience a number of relatively violent quakes every year.

But building codes are rigorous and regular disaster drills are held, helping to ensure that despite their frequency and magnitude, earthquakes usually pass without loss of life or significant damage to property.