At least 26 coal miners were trapped in a mile-long tunnel 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.
President Hassan Rouhani sent Minister of Labour and Welfare Ali Rabii to the site, ISNA News agency reported.
A provincial Red Crescent official, Shahin Fathi, rejected early figures of 80 miners trapped and said the number was 26 based on latest information.
He said there was no information on the condition of those inside adding that workers sent to hospital were among those who had rushed to help after the blast.
Some 25 miners were treated for gas poisoning and injuries, Fathi added.
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.