A rock outburst that occurred in a coal mine in Northeast China's Heilongjiang Province early Friday morning has trapped 20 workers underground, local authorities said.

Twenty-eight miners were working in the Junde Coal Mine in the city of Hegang when the accident happened around 5:20 am Friday. Eight of the miners were lifted out of the mine, according to sources from the municipal government.

Rescuers have established contact with 16 of the 20 trapped miners and determined that they are safe for the time being, the sources said.

The coal mine is owned by the state-owned Heilongjiang Longmay Mining Holding Group.

Rescue efforts are under way.