Buildings swayed for around a minute in Tokyo and its vicinity last night as the quake struck at a remote spot in the Pacific Ocean around 874 kilometres south of the capital, the US Geological Survey said.

Despite its power, there was no risk of a tsunami as its epicentre was a deep 676 kilometres below the Earth's surface, the USGS and the Pacific Tsunami Warning Center said.

Twelve people were injured, including a 56-year-old man who broke his ribs, but no one was killed, an official of the Tokyo Fire Department and local media said today.

Some 400 people were trapped at the observation decks of Tokyo Tower as its elevators stopped for more than one hour.

Runways at Haneda Airport in Tokyo were closed for about 30 minutes, with trains also temporarily halted, while a football match in the city was briefly suspended.

There were no reported anomalies at any of the region's mothballed nuclear power plants.

A massive undersea quake that hit in March 2011 sent a tsunami barrelling into Japan's northeast coast, killing thousands of people and sending three reactors into meltdown at the Fukushima nuclear plant.

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

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