The quake with a preliminary magnitude of 6.7 hit about 12:30 pm (0330 GMT) today, near Urakawa town on the southern tip of Hokkaido, according to the Japan Meteorological Agency.

It said the quake's center was located at a depth of 50 kilometers (30 miles) below the sea surface.

There were no immediate reports of injuries or damage. The lunchtime quake caught many residents by surprise.

"It was pretty strong. It went on about 40 seconds," said Haru Matsutakeya, 45-year-old resident in Hokkaido's capital of Sapporo, about 170 kilometers (100 miles) northwest of the epicenter.

Two nuclear power plants and the Rokkasho reprocessing plant in the quake-hit region were not affected, nuclear safety officials said.

Tohoku 'bullet train' service south of the region was temporarily suspended but has since resumed, according to NHK.

Some local train lines in Hokkaido were suspended for safety checks, though there were no immediate reports of damage.

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