Two men have died after being found unconscious in an underground tunnel at a copper mining museum in Murdochville, on Quebec's Gaspé peninsula.

Emergency responders were called around 9:30 Tuesday morning and firefighters were sent in with special equipment, because of a suspected gas leak. When the firefighters entered the tunnel they found the two men unconscious, one lying on top of the other.

The men were rushed to hospital, where they were later declared dead.

One of the men was an 50-year-old employee and the other was a 60-year-old volunteer.

According to André Minville, the town's director of fire services, the men may have been poisoned by carbon monoxide gas from a pump that was being used to clear water out of the tunnel.

André Minville, the director of the town's emregency services, said that the two men were found unconscious, one lying on top of the other, in a tunnel under the museum. (Martin Toulgoat/Radio-Canada)

The tunnel wasn't accessible to visitors and had apparently flooded during winter after a power outage.

The museum had only re-opened one week ago. It was partially destroyed by a fire in 2012, then closed because of a $120,000 deficit.

Murdochville's mayor, Délisca Ritchie-Roussy, called it a tragedy.

"We lost two committed citizens who wanted to revive the museum. That's why they were trying to empty the tunnel, so that it would be accessible as quickly as possible for tourists," she said.

The Sûreté du Québec's major crimes unit is investigating, and so is the province's workplace health and safety board, the CNESST.

Two inspectors are on the scene, according to a spokesperson for the CNESST.