A strong earthquake with a preliminary magnitude of 6.1 has jolted Tokyo and surrounding areas, stopping train lines and causing sporadic power cuts, but there were no reports of major damage, Japan's public broadcaster says.
The tremor, at 10.41pm, 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 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 power outages 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.
Australian Associated Press