A natural gas explosion at a shopping mall in southwestern China has killed four people and injured 35 others.

The Luzhou municipal government in Sichuan province says three floors of the Moerma shopping center caught fire after the explosion late Thursday. Its online statement says there were four deaths and 35 people injured as of Friday morning.

Local authorities cordoned off the area and urged residents not to gather to look at the scorched structure. News photos show shattered glasses and blackened wall panels.

The city government says the cause of the explosion is under investigation.

Workplace safety is a major problem in China, where safety regulations are often ignored.