The quake hit at 12.24 pm local time (0324 GMT), 337 kilometres (210 miles) west northwest of Chichi-shima in Japan's remote Bonin island region at a depth of 478 kilometres. There were no immediate reports of damage or injury.

The USGS originally said the quake was magnitude 6.9, but later revised its figure.

Japan's meteorological agency also said the focus was off the west coast of the same chain of islands in the Pacific, known in Japan as the Ogasawara islands, 808 kilometres south of Tokyo.

Even so, the quake swayed buildings in the capital.

Around 20 percent of the world's most powerful earthquakes strike Japan, which sits on the "Ring of Fire" surrounding the Pacific Ocean.

But high building standards, regular drills and a sophisticated tsunami warning system mean that casualties are often minimal.

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