At least 70 coal miners were trapped after an explosion in northern Iran on Wednesday, Iranian media said.

The mine in Golestan province collapsed when trapped methane gas exploded as workers tried to jump-start a locomotive engine, according to reports.

"Forty workers are trapped in one part of the mine and another 30 to 40 are trapped in another part," the Fars and ISNA news agencies quoted the head of Iran's emergency services, Pir Hossein Kolivand, as saying.

Twelve injured miners were pulled out alive, he said.

A local official said the tunnels were filled with gas, making rescue work difficult.

"Work to remove the rubble and drilling for a side tunnel has begun to access the trapped workers in the Zemestan Yort mine," the official said.

Another official who did not want to be named told state news agency IRNA that several workers probably died in the blast, but there was no official casualty toll.

The mine has 500 workers and the explosion happened during a change of shift, state media said.

Emergency teams and sniffer dogs have been dispatched to the mine and work to remove the rubble has begun.