HARBIN - A forest fire that broke out in North China's Inner Mongolia autonomous region Saturday has spread to neighboring Heilongjiang province, local fire authorities said Monday.

The fire started in the Hanma National Nature Reserve in the northern area of the Greater Hinggan Mountains Saturday, and spread to Heilongjiang by Sunday afternoon.

The current size of the fire is hard to detect due to heavy smoke.

More than 3,600 firefighters, forest police and items of large fire fighting equipment have been mobilized. Artificial precipitation is being used to help put out the fire.

The fire is not yet under control.