A truck loaded with firecrackers blew up in southern China (search) Thursday, killing at least 20 people, some who were on a nearby bus, the government said.

Another seven bystanders were injured in the blast on a highway near Shangrao (search), a city in Jiangxi province, the official Xinhua News Agency said.

"The exact death toll is still unavailable, as the victims were blown to pieces," the agency said, citing police, who estimated that up to 30 people might have been killed.

The truck had been carrying firecrackers from Liuyang in the central province of Hunan, a major firecracker producer. Investigators initially thought the explosion originated on the double-decker bus, Xinhua said, but did not provide any other details.

The cause of the explosion was still under investigation, it said.