An initial investigation has shown that a fire that broke out on a national nature reserve in northwest China's Gansu Province was caused by a lightning strike, local authorities said Wednesday.

The fire is still raging in one area of the Liancheng National Nature Reserve in the provincial capital of Lanzhou, while fires in two other areas were put out by Wednesday morning, Duan Changsheng, deputy chief of the provincial Forestry Department, said at a press conference.

About 1,000 firefighters are battling the blaze. Five cloud-seeding rocket launchers are on standby to create artificial rainfall once conditions permit, said Lanzhou municipal government representative Wei Qingxiang.

The fire was first reported on Tuesday, when it had already engulfed an area of 60 hectares.

Rugged terrain and thick vegetation have hindered firefighting efforts. Firefighters have resorted to using small fire extinguishers and creating "buffer zones" to curb the fire, said Wei.

The Liancheng National Nature Reserve, located 140 km away from the provincial capital of Lanzhou, covers an area of 48,000 hectares between the Qilian Mountains and the Loess Plateau.