More than 50 workers are trapped in a coal mine after a suspected gas explosion blocked their paths in Iran’s Golestan province on Wednesday, state media reports said. Reports said an attempt to start a lorry engine may have triggered the explosion.

At least 25 are reportedly wounded at the Zemestan-Yurt mine. An official said 16 people had managed to escape. The head of Iran’s emergency services, Pirhossein Koulivand, said the number of victims may be much higher.

Concerns about the presence of a poisonous gas within the tunnels have hindered the rescue process, BBC reported. At least 25 rescue personnel are undergoing treatment after inhaling the substance, Hamidreza Montazeri, deputy head of the provincial emergency services, told Iran’s PressTV.

Iran is highly dependent on its domestic coal supply as the bulk of it is used in steel production. In 2016, the country extracted 1.68 million tonnes of coal, BBC reported