People receive supplies in Mashiki, Kumamoto prefecture, on April 15, 2016, after a M6.5 quake shaked the town the previous night. [Photo/IC]

Japanese media showed residents, some of them wrapped in blankets, huddling in parking lots and other open space for fear of further building collapses.

"The apartment building I live in is now tilting. Everything fell down inside. It's a mess," a male resident in Mashiki said on NHK.

About 16,500 households in and around Mashiki were without electricity as of 2 am (1700 GMT), according to Kyushu Electric Power Co Inc.

The Nuclear Regulation Authority said there were no irregularities at three nuclear plants on the southern major island of Kyushu and nearby Shikoku.

In March 2011, a quake of magnitude 9 struck offshore north of Tokyo, causing tsunami waves along the coast that killed nearly 20,000 people and triggered a nuclear power plant meltdown.