A powerful earthquake with a magnitude of 6.4 knocked over houses in southern Japan on Thursday and police said people may be trapped underneath.

Japanese Red Cross Kumamoto Hospital said it has admitted or treated 45 people, including five with serious injuries.

“The shaking was so violent I couldn’t stand still,” said Hironobu Kosaki, a Kumamoto prefectural police official.

He said they had received reports of collapsed houses and people possibly trapped inside.

The Japan Meteorological Agency said the quake hit at 9:36 pm (12:36 GMT) at a depth of 10 kilometres. No tsunami warning was issued.

The quake measured the highest of 7 on Japan’s intensity scale in Mashiki town, 900km southwest of Tokyo, the meteorological agency said.

“We intend to do the utmost to grasp the situation,” Prime Minister Shinzo Abe told reporters. “I’m now planning to hear what we have gathered on the situation.”

Broadcaster NHK said more than 10 buildings had collapsed in Mashiki town, with a population of about 34,000, and a fire had broken out.

Some 16,000 households in the area were without electricity, Japanese media reported.

At least one aftershock struck the region.

Kyushu Electric Power said there was no impact of the quake on two nuclear reactors at the Sendai Nuclear Power Station in Kagoshima prefecture, according to broadcaster NHK.

The plant is 130km south of Kumamoto city. The operator restarted the reactors last year, the first two units under updated regulations.

The quake prompted the suspension of train services in the region, according to NHK.

In March 2011, a 9.0-magnitude earthquake sparked a devastating tsunami that killed 18,000 people along Japan’s northeast coast.

The massive wave struck the Fukushima nuclear plant, causing a major radiation leakage.

More than 100,000 displaced people are still unable to return to their homes near the nuclear plant because of the contamination. (Al Jazeera and News Agencies)

•Photo shows rescue workers evacuating the injured after Thursday’s earthquake in southern Japan.