A?forest fire raged on a mountain in Chengde city, Hebei province,?northeast of Beijing?on Tuesday. [Xinhua]

More than 2,000 people are struggling to put out a forest fire that has been raging on a mountain northeast of Beijing, local authorities said on Tuesday.

Steep hills, strong winds and poor telecommunications have added difficulties to the efforts to control the blaze, which started on a mountain in Chengde city, Hebei province, at about 1 pm on Monday, according to a spokesman for the province's forest fire control authorities.

The cause of the fire remains unclear, he said.