A magnitude 7.8 earthquake struck off Japan's coast on Saturday, according to United States Geological Survey (USGS), but there were no immediate reports of damage, public broadcaster NHK said.

Despite the huge power of the quake, there was no risk of a tsunami "because the earthquake is located too deep inside the earth", according to the Pacific Tsunami Warning Centre.

Residential buildings in Tokyo swayed for around a minute as the quake built in intensity around 8.30pm local time (9:30pm AEST).

The epicentre was 676 kilometres below the Earth's surface and was centred on a remote spot in the Pacific Ocean around 870 kilometres south of Tokyo, the USGS said.

The Japan Meteorological Agency said the earthquake had a magnitude of 8.5 at a depth of 590 kilometres.

Yoshiyuki Sasamoto, who runs a traditional guest house on Chichijima, one of the closest inhabited places to the epicentre, told NHK the shaking had been violent.

"Initially a weaker quake hit and it stopped. Then the big one came. It was so strong that I couldn't stand still and couldn't walk," he said.

A supermarket aisle in Kawaguchi city, immediately north of Tokyo, after the earthquake hit. ( Supplied: Alan Nishimura )

Both runways at Narita Airport, the main international gateway to Tokyo, were temporarily closed while inspections were carried out.

Trains in Tokyo were also temporarily halted and a football match in the city was briefly suspended.

Tokyo Electric Power Company (TEPCO) said there were no abnormalities at the crippled Fukushima nuclear power plant following the quake.

A massive undersea quake that hit in March 2011 sent a tsunami barrelling into Japan's north-east coast.

As well as killing thousands of people and destroying communities, the waves also swamped the cooling systems at Fukushima, sending three reactors into meltdown.

The nuclear disaster, the world's worst since Chernobyl, displaced tens of thousands of people and rendered tracts of land uninhabitable, possibly for decades.

Saturday's quake was the second sizable shake Tokyo has had this week, after a much less powerful, but far shallower quake hit close to the capital on Monday.

Japan sits at the meeting place of four tectonic plates and experiences around 20 per cent of the world's most powerful earthquakes every year.

On Friday, a volcano in the far south of Japan erupted, spewing a huge column of ash high into the sky and forcing authorities to evacuate the island on which it sits.

The eruption caused no injuries and no damage was reported, but it served as yet another reminder of the volatile geology of the country.

AFP