BEIJING - The fire at a Beijing power plant on Friday afternoon was caused by a blast of the generator unit, an initial investigation showed.

It was a work safety accident, said Beijing fire authorities.

The power plant is operated by one of China's leading power producers, Huaneng Group. No casualties were reported.

The blast happened at the No 2 generating unit of the plant, when the hydrogen used for cooling and the oil in operation triggered the explosion. It led to the shutdown of all the four units.

Local police said their helicopters noticed smoke coming from the thermal power plant in Chaoyang District during routine patrol at around 2:50 pm Friday. They dispatched rescuers and 91 fire engines to the site.

Further investigation into the cause of the blast continues.

The plant was put into operation in 1999.