CHANGSHA, May 7 (Xinhua) -- Five people have been killed and three others were injured after an explosion in the office of a colliery in central China's Hunan Province, sources with the local work safety bureau said Monday.

The explosion occurred around 6:40 p.m. Sunday in a building housing the office in the Zhalin coal mine, Jiahe County, said LiuShiyuan, director of the county work safety bureau.

Seven people were in the office when the explosion happened. The blast injured two passers-by and a boy from a nearby village who was playing in the mine area, he said.

They are being treated in a local hospital, Liu said.

"We have finished clearing debris, and the accident may have been caused by explosives stored in the office. We will have to carry out further investigation to decide the exact cause," Liu said.