The reports place the explosion at 12:45 pm local time (8:15 am GMT).
Some of the trapped miners may have died in the explosion, IRNA state news agency cited a local official. A rescue operation was under way.
More than a dozen injured people had been transferred to hospital after the blast in the Zemestanyurt coal mine in Golestan province, local media reported.
Some reports say that as many as 80 miners had been trapped in the explosion.
Over 500 miners work at the Zemestanyurt coal mine, which lies 14 km of Azadshahr city, situated in 90 km east of Gorgan, the capital city of Golestan Province.
The cause of the explosion has not yet been determined.