The blast happened at 12:45pm, at a time when workers were changing shifts. Some 50 injured miners have been so far taken out of the mine.
Several officials blamed the explosion on accumulated gas and said it was affecting rescue efforts.
Hamidreza Montazeri, deputy head of Golestan province's emergency services, said that 25 people, who had entered the mine to help the trapped miners, had been taken to hospital due to gas inhalation.
LR