KUNMING - More than 500 fire fighters, policemen and local residents are trying to quench a forest fire in Kunming, capital city of Southwest China's Yunnan province, local authorities said Monday.

The fire broke out around 4 pm in the Xishan district, Kunming, sources with the Kunming forest fire prevention commanding center said.

More than 500 people, including 140 forest policemen, have been mobilized to quench the fire, according to the sources.

An investigation into the cause of the fire is under way.