The death toll from a chemical plant blast in southwest China's Guizhou Province has risen to six after a worker died of severe burns in hospital, local authorities said Friday.

The explosion ripped through the Yihua Chemical Co. Ltd. in Xingyi, in the Bouyei-Miao Autonomous Prefecture of Qianxinan, at about 9 a.m. Thursday, killing five people instantly.

"The explosion occurred when workers were repairing chemical material pipelines," said Chen Gang, director of the prefecture government's emergency response office.

"An initial investigation shows that the explosion was triggered by a leak of mixed gas, including carbon monoxide, carbon dioxide, hydrogen and nitrogen," he said.

Five other workers were still being treated in hospital, he said, without specifying their conditions.