NANNING - An explosion killing six people at a snack stall in South China's Guangxi Zhuang autonomous region Thursday night has prompted a safety overhaul to remove potential risks, local authorities said Friday.

The explosion went off at 9:30 p.m. at an outdoor snack stall near a supermarket in Ningming County, in the city of Chongzuo, the county government said in a midnight press release.

It said three people were killed at the scene and three others were confirmed dead later in hospital.

Of the 18 people injured, two were still in critical condition as of Friday morning, an official with the county government told Xinhua in a telephone interview Friday morning.

He said gas leak from the burner was suspected to have caused the accident, but investigation was still underway.

The county government launched a safety overhaul shortly after midnight, sweeping local markets, cafeterias and other public places to detect and remove potential risks.