Dozens of people were injured after a 6.4-magnitude earthquake struck Japan's southern island of Kyushu on Thursday, local media reported.
The quake struck at 9:26 pm (1226 GMT) at a depth of 10 kilometres, with its epicentre in the Kumamoto region, but no tsunami warning was issued, the Japan Meteorological Agency said, adding that more than 10 aftershocks were reported in the two hours after the quake.
Another magnitude-6.4 quake, considered to be one of the aftershocks, struck several hours later at 0:03 am Friday (1503 GMT), the agency reported.
The quake collapsed walls and a number of houses in the town of Mashiki, 900 kilometres south-west of Tokyo. People could be trapped, and one of them was unconscious, according to broadcaster NHK.
Japan's military has dispatched aircraft and helicopters to the quake-struck region to assess the extent of damage, Defence Minister Gen Nakatani told a news conference.
Chief Cabinet Secretary Yoshihide Suga urged those affected to remain calm and to help each other. He also said that there no abnormalities reported at the Genkai Nuclear Power Plant in Saga prefecture or the Sendai Nuclear Power Station in Kagoshima prefecture.
The Sendai plant is 130 kilometres south of Kumamoto. The operator restarted two nuclear reactors last year, the first of two units under updated regulations.
The quake prompted the suspension of train services in the region, according to NHK.