SHIJIAZHUANG - Nineteen people have been punished after trying to cover up an explosion that killed seven workers and injured another in July in North China's Hebei province, investigators said Thursday.

The 19, including government officials in charge of safety and quality supervision, a legal representative and other senior managers of the Xingang Steel Group, received penalties ranging from criminal detention to fines, said a written statement released by the investigation team.

Another two workers, Wang Zengqiang and Li Ming, who were responsible for the explosion, were killed in the accident, said the statement.

The explosion happened at 7 am on July 30, when workers were repairing the pneumatic diaphragm control valve at the group's oxygen-making plant in Wen'an county in the city of Langfang.

Four people were killed at the scene and three others died later in hospital. The injured person remains in hospital in Langfang. The blast caused economic losses of up to 12.9 million yuan ($2.1 million).

Investigations by provincial and city authorities found Wang and Li were carrying out repair work without following national regulations. This resulted in oxygen being released through the valve, triggering the explosion.

Following the accident, the company was found to have transferred the bodies of the dead to cover up the accident. Police were informed of what happened by local residents.