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TOKYO (Reuters) - An earthquake with a preliminary magnitude of 6.6 shook western Japan on Friday, the Japan Meteorological Agency said, adding that a tsunami warning was not issued.

There were no immediate reports of injuries or major damage and no irregularities at nuclear plants, but media said roughly 40,000 households were at one point without power.

Gravestones were toppled, bottles fell off store shelves and smashed, and at least one building collapsed. There were no reports of deaths or major injuries, and nobody was trapped, Chief Cabinet Secretary Yoshihide Suga told a news conference.

The epicenter of the earthquake was in Tottori prefecture at a depth of 10 km (6 miles), the agency said. The quake occurred at 2:07 p.m. and was followed by a series of weaker aftershocks.

The Japan Atomic Energy Agency, a government-backed nuclear research institute, said connection to outside power at a partly-decommissioned experimental uranium extraction facility was lost for 53 minutes, but auxiliary generators turned on immediately so there was no loss of power or damage.

On March 11, 2011, the northeast coast was struck by a magnitude 9 earthquake, the strongest quake in Japan on record, and a massive tsunami. Those events triggered the world’s worst nuclear crisis since Chernobyl a quarter of a century earlier.

Earthquakes are common in Japan, one of the world’s most seismically active area. Japan accounts for about 20 percent of the world’s earthquakes of magnitude 6 or greater.