Some 2,000 people in Southwest China's Yunnan Province are working to put out a forest fire that broke out early on Thursday morning, local authorities have said.

The fire erupted around 2:30 am at the Yangzonghai forest farm in Yiliang county, Kunming city, said an official with the Kunming municipal forest fire prevention headquarters.

Topography conditions are complicated at the site, and the fire was yet to be controlled by 11 am, the official said.

Forest police, professional fire-fighting teams and residents are joining the efforts to put out the blaze.

The cause of the fire is under investigation.