Three government officials and two executives have been sacked or detained over a fireworks factory explosion that left 20 people dead in northeast China, local authorities said Wednesday.

Four people are still missing and 153 were injured after the explosion ripped through the fireworks factory in the Wumahe District of Yichun City, Heilongjiang Province, Monday.

Zhao Weiqiang, deputy head of the Wumahe District, who is in charge of work safety, and Cheng Chuanxin, head of the Wumahe District Work Safety Bureau, had been removed from their posts, according to a statement from the Yichun City Committee of the Communist Party of China on Wednesday.

Police had detained Liu Chunya, a safety inspector at the bureau, for dereliction of duty, according to the statement.

Jin Chaoxiang, head of the fireworks factory, and Zhou Shiji, deputy head of the factory, had also been detained, it said.

The cause of the accident was still under investigation.

A preliminary investigation showed the plant was illegally producing fireworks, as its production permit was confiscated in June by the local work safety department, said a statement issued Tuesday by the State Administration of Work Safety.

The plant was requested in June to suspend production and improve safety standards, said the statement.