The quake hit at 2:53 am (1753 GMT Friday) and there were no immediate reports of casualties or damage, Kyodo said.

The agency said the focus of the quake was about 10 kilometers underground in the Chuetsu area.

The latest quake is believed to be an aftershock to the October 23 quake in Niigata, 200 kilometres (125 miles) northwest of Tokyo, which registered 6.8 on the Richter scale and was followed by hundreds of aftershocks. Thirty-nine people have died, with more than 3,000 injured.

Elsewhere in Japan, an earthquake measuring 4.3 on the Richter scale struck off the coast in the northern Iwate prefecture Friday, but there were no reports of damage or injuries.

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