Fire fighters extinguish fire on the Daheishan Mountain in Dalian of Northeast China's Liaoning province March 22, 2015. The mountain caught fire 2pm on Sunday. [Photo/CFP]

A forest fire that killed five mountaineers raged for more than four hours in northeastern coastal city of Dalian on Sunday.

At the time of writing, more than 300 firefighters fought to contain the blaze on Daheishan Mountain, about 500 meters away from the nearest habitation, according to the Dalian Evening News.

Pictures showing hills engulfed in thick smoke were circulating online.

The newspaper quoted a rescue worker as saying that unscrupulous use of fire during picnicking could be a likely cause.