People gather at a hotel lobby after an earthquake in Kumamoto, southwestern Japan, April 16, 2016. Kumamoto Prefecture in southwestern Japan was hit again by a magnitude-7.1 earthquake on Saturday at 1:25 local time. (Xinhua/Liu Tian)

OSAKA, April 16 (Xinhua) -- At least 22 people have been confirmed dead after a 7.3-magnitude earthquake rocked Japan's southwestern Kumamoto Prefecture on Saturday, bringing the total number killed since Thursday to 31.

Local government officials said that at least 22 people were dead and over 1,000 injured as a result of the powerful earthquake that hit Kumamoto in the early hours of Saturday.

The death toll is still expected to rise, as search and rescue operations are under way.

The quake struck at 01:25 local time (1625 GMT Friday) and was upgraded from a provisional magnitude of 7.1 to 7.3, with the temblor being felt across wide swathes of southern Japan and triggering a tsunami warning which was later lifted.

Numerous aftershocks followed, including three severe ones graded upper 6 or lower 6 on Japanese seismic scale.

Local media also reported a "small-scale" eruption at Mount Aso, a large active volcano in Kumamoto. The Japanese Meteorological Agency said that it was not clear how the eruption was linked to the quakes.

The agency also said that Saturday's massive earthquake was the main event while the one on April 14 was a foreshock.

A 6.5-magnitude quake hit southwestern Japan Thursday night, killing 9 and injuring over 950 others.

The quakes triggered blackout affecting about 200,000 households in the region. Water supply has been cut off in Kumamoto city and parts of the Oita prefecture, affecting 680,000 families.

Dozens of people have been reported trapped or buried alive under collapsed buildings or landslides, including 11 college students trapped in the rubble of four collapsed buildings in Minamiaso. Rescue efforts are under way.

Traffic was halted on some expressways in Kumamoto and Miyazaki Prefectures and parts of local roads were damaged. All flights from Kumamoto Airport on Saturday have been cancelled, said local reports.

No abnormalities were observed at the Sendai nuclear power plant, the only operating nuclear facility in the area, said local reports.

The Japanese weather agency warned that severe aftershocks measured lower 6 on the Japanese scale might still follow and as heavy wind and rain was predicted in the Kyushu area from Saturday night, residents should be wary of landslides and other secondary disasters.