An explosion caused by illegally stored chemicals has killed seven people and injured 37 at an Internet cafe in southwest China, state media and the government said Sunday.

The blast occurred late Saturday in a shop next to the cafe, located under a bridge, the Kaili city government in Guizhou province said in a statement. The official Xinhua News Agency said nine of those hurt were seriously injured.

Six people were killed on the spot and one woman died of extensive burns Sunday after treatment at a hospital failed, Xinhua said. Investigators are identifying the bodies, which included one child, the report said.

Packs of highly concentrated aluminum chloride and sodium nitrite, which are hazardous, were stacked up against a wall in a shop that sold chemicals adjacent to the Internet cafe, the report said. It did not say how the chemicals were ignited.

Police have detained a person named Wu Zhanzhi for illegal possession of the chemicals, while the cafe's boss and manager were also being held by police for questioning, it said. The explosion was so powerful it shattered the windows of nearby residential buildings, Xinhua said.