An explosion rocked a small apartment block, waking the residents, and leaving four people severely injured in southern Vietnam on Tuesday.

Preliminary examination concluded that manhole gas was to blame.

The incident took place at 5:00 am at a small apartment block in Thu Dau Mot City, Binh Duong Province.

Residents reported a loud bang coming from the rear of the apartment block, followed by a terrifying scream from room No. 8.

Four occupants in the room were found injured and immediately rushed to the nearest hospital.

They are Le Thanh Phong, 37, his wife Truong Thi Hong Dao, 34, their 10-year-old son Le Dang Khoi, and 3-year-old daughter Le Thi Kim Han.

Phong and Dao were seriously injured and suffered severe burns.

The explosion peeled off a part of the corrugated iron roof and left many housewares blown to bits and scattered around the room.

Colonel Nguyen Van Minh, chief police officer of Thu Dau Mot City, said that the possible cause of the explosion was manhole gas coming from the apartment’s septic tank after examining the scene.

“Accumulation of trapped manhole gas in the septic tank fueled the explosion. There are no other threats from gas leakage or other flammable materials,” Minh said.

It is likely that a cigarette ignited the flammable gas mixture.

Experts concluded their primary examination of the explosion scene at 9:30 am the same day.

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