Two firefighters were killed in an unexpected explosion while putting out fire in a power company in Beijing's Fengtai District, municipal authority said on Saturday.

The blaze erupted on Friday at 12:17 p.m. and a total of 235 firefighters and 47 fire trucks were sent to put out the blaze.

On Friday afternoon at around 2:15 p.m., a sudden explosion occurred on the north section of the power company, killing two officers and injuring another one, the authority said in a statement.

One company staffer is also missing, it added. 

An online video shows massive black smoke billowing from the site. But no open flames were seen by Friday midnight. 

Relevant departments in Beijing are now conducting safety check in nearby areas around the fire site and calculating damages from the accident.