The quake measuring 5.2 percent on the Richter scale occurred 20 kilometres (12 miles) underground in Niigata prefecture, some 200 kilometers (125 miles) northwest of Tokyo, the Meteorological Agency said.

The rice-growing region was hit by a 6.8 magnitude quake on October 23, followed by hundreds of aftershocks which have forced more than 50,000 people to abandon their homes for temporary shelters.

In the town of Tochio, 71-year-old shopowner Yokichi Tamura died at a hospital from a heart attack caused by the "stress" of 11 days in a shelter, prefectural police said.

At least 3,183 people were also injured in last month's quakes, the National Police Agency said.

Tokyo Electric Power Co. said a reactor at the seaside Kashiwazaki-Kariwa nuclear power plant automatically shut down when Thursday's tremor hit.

The reactor was down for hours but there was no radioactive leak, a company spokesman said. Five other reactors at the plant continued operations with another reactor closed for regular check-ups.

A bullet train linking Niigata with Tokyo ground to a halt during the quake but no passengers were injured.

The Meteorological Agency warned residents to brace themselves for more strong quakes.

"They need to be on the alert at least for the coming month," said Masahiro Yamamoto, who heads the earthquakes division of the agency.

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