A forest fire broke out Saturday morning on a nature reserve in the Greater Hinggan Mountains in northeast China's Heilongjiang Province, local authorities said.

The fire remained out of control as of 12:00 p.m., local forest fire prevention authorities said.

Nearly 6,300 people have been mobilized to extinguish the fire, the provincial forest fire prevention headquarters said.

Local authorities said a smoke column was first spotted on the Nanweng River Nature Reserve at 9:30 a.m. Saturday. A satellite monitoring report confirmed the fire's location later.

No casualties have been reported.

The cause of the fire remains unclear.