Firefighters battling a fire in the Greater Hinggan Mountains (Photo taken by Global Times)

HOHHOT, May 2 (Xinhua) -- Hundreds of firefighters are battling a fire in China's largest forest in the Greater Hinggan Mountains.

The fire broke out at 12:15 p.m. Tuesday in the Bilahe Beidahe forest in north China's Inner Mongolia Autonomous Region, said regional fire authorities.

As of Tuesday afternoon, the fire had engulfed about 500 hectares of forest. More than 1,300 firefighters and four helicopters have been sent to extinguish the blaze. Strong winds and mountainous terrain are making their work difficult.

The cause of the fire is unknown.

The temperature in Inner Mongolia this spring is higher than previous years, posing a higher fire risk for the region's forests.

A fire broke out Sunday in another forest in the area. It has been put out and cleanup is underway.