A strong earthquake with a preliminary magnitude of 6.1 jolted Tokyo and surrounding areas late on Thursday, stopping train lines and causing sporadic power cuts.
But there were no reports of major damage, Japan's public broadcaster NHK said.
The tremor, at 10:41 p.m. (1341 GMT), registered "strong-5" on Japan's intensity scale, a level that could cause some damage to buildings and power cuts, the Japan Meteorological Agency said.
The quake had an epicentre in Chiba prefecture, to the east of the capital Tokyo. There was no danger of a tsunami from the quake, NHK said.
The government has set up an emergency response task force.
NHK showed new Prime Minister Fumio Kishida rushing back to his office. He told reporters he had instructed the task force to "find out about the latest situation, coordinate with local authorities on response", and to provide information to the public in a speedy manner.
Several minutes earlier Kishida tweeted: "Take actions to protect your lives while confirming the latest information."
Private broadcaster TBS reported incidents of water pipes bursting in Tokyo. Tokyo Electric Power Corporation reported 250 cases of blackouts in the city.
Earthquakes are common in Japan, one of the world's most seismically active areas. The country accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.
On March 11, 2011, the northeast coast was struck by a magnitude 9 earthquake, the strongest in Japan on record, and a massive tsunami.
Those events severely damaged the Fukushima Daiichi nuclear power plant, triggering the world's worst nuclear crisis since Chernobyl a quarter of a century earlier
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