A man is carried away by a rescue workers after being rescued from his collapsed home caused by an earthquake in Mashiki town, Kumamoto prefecture, southern Japan, in this photo taken by Kyodo April 16, 2016. [Photo/Agencies]

TOKYO - A magnitude 7.3 earthquake struck southern Japan early on Saturday, killing at least 32 people, injuring hundreds more and trapping people in collapsed buildings, media reported, just over a day after a quake killed nine people in the same region.

Authorities warned of damage over a wide area with reports of fires, power outages, collapsed bridges and gaping holes in the earth. Residents near a dam were told to leave because of fears it might crumble, broadcaster NHK said.

Saturday's quake triggered a tsunami advisory, although it was later lifted and no irregularities were reported at three nuclear power plants in the area, a senior government official said. There were at least 50 aftershocks from Saturday's quake.

People still reeling from Thursday's shock poured onto the streets after the Saturday earthquake hit at 1:25 am (1625 GMT).

TV Asahi showed rescue efforts for what it said were 11 trapped people in a university apartment in the town of Minami Aso.

A fire erupted in a what appeared to be an apartment building in Yatsushiro city, while some people were trapped in a nursing home in the town of Mashiki, according to NHK.

Hotel guests gather at the lobby after another earthquake hit the area in Kumamoto, southern Japan, in this photo taken by Kyodo April 16, 2016. [Photo/Agencies]

Shallow depth 10 kms

NHK reported 11 deaths and 760 people treated in hospitals, but that figure included "people who don't feel well", so it was not clear how many serious injuries there were.

Chief Cabinet Secretary Yoshihide Suga said nearly 80 people were believed trapped or buried in rubble. Extra troops would be sent to help, with up to 15,000 due on Saturday, as well as more police, firefighters and medics, he said.

"We are making every effort to respond," Suga said.

Troops fanned out to search ruined houses as dawn broke.

The epicenter of the quake was near the city of Kumamoto and measured at a shallow depth of 10 kms (6 miles), the US Geological Survey said. Almost 200,000 households were without power.

Local residents look at cracks caused by an earthquake on a road in Mashiki town, Kumamoto prefecture, southern Japan, in this photo taken by Kyodo, April 16, 2016. [Photo/Agencies]

Public transport service halted

The Japan Meteorological Agency initially said the Saturday quake was 7.1 magnitude but later revised it up to 7.3. The quake was 22 times more powerful, in terms of energy released, than Thursday's shock, according to the USGS website's "Magnitude Difference Calculator".

The region's transport network suffered considerable damage with one tunnel caved in, a highway bridge damaged, roads blocked by landslips and train services halted, media reported. Kumamoto airport was also closed.

Forecast heavy rain in the coming days could cause more landslides and affect already damaged structures, said the meteorological agency.