TOKYO (REUTERS) - An earthquake with preliminary magnitude of 6.8 jolted central Japan on Saturday evening, temporarily trapping 21 people when their homes collapsed and leaving 13 people injured, police and public broadcaster NHK said.
The Japan Meteorological Agency said no tsunami warning was issued after the quake, which was felt in the capital Tokyo 180km away.
A National Police Agency official said the quake destroyed five houses in Hakuba village, host to ski jumping and other events during the 1998 Nagano Winter Olympic Games, but that the 21 villagers trapped were successfully rescued.
At least two of them were injured, although the degree of their injuries was not immediately clear, he said.
NHK reported 13 people were injured in the quake, including five who were seriously hurt.
Chief Cabinet Secretary Yoshihide Suga told reporters an advanced party of Japan's military had been sent to the area, and others were on standby.
High-speed trains were halted but later resumed service, Kyodo news agency reported.
There were no signs of irregularities at Tokyo Electric Power Co's Kashiwazaki Kariwa nuclear plant, a spokesman for the utility said. The plant, where all seven reactors are currently off-line, is the world's largest power station.
NHK quoted an official in the village of Ogawa near the epicentre as saying there was a long tremor and documents fell off shelves.
"On the second floor of our house, the tremor was too strong to stand," said Sakiko Hagiwara, an NHK employee in the area.
"Pictures fell off the wall," she said, adding there were no cracks in the walls.
NHK also said there was a report of a landslide blocking roads near Hakuba.
Japan, situated on the "Ring of Fire" arc of volcanoes and oceanic trenches that partly encircles the Pacific Basin, accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.
On March 11, 2011, a 9.0 magnitude earthquake struck under the ocean off the coast of the northern city of Sendai.
The quake triggered a massive tsunami that devastated a wide swathe of the Pacific coastline and killed nearly 20,000.
It also devastated the Fukushima Daiichi nuclear plant, causing meltdowns in the world's worst nuclear disaster in 25 years.