The workers, who all have extensive burns, were flown to Brisbane overnight in a complex medical evacuation involving five planes.

Four remain in a critical condition and had to be ventilated to help them deal with damage to their airways, the ambulance service said.

The blast rang out at the Grosvenor Coal Mine at Moranbah in central Queensland on Wednesday afternoon, with the mining union saying a gas ignition along the coalface appears to be to blame.

Doug Buchanan from the Queensland Ambulance Service said teams of nurses and doctors worked on the men as they were flown from the Moranbah Hospital to Brisbane.

Four of the men “required urgent specialist care for their repatriation”, he said. Those men were critical, with the fifth victim in serious condition.

All five are now receiving specialist care in the Royal Brisbane and Women’s Hospital.

Mine operator Anglo American has evacuated the worksite, and all other employees have been accounted for.

The mine will remain closed on Thursday, as inspectors work out what happened.

Queensland’s Chief Inspector of Coal Mines Peter Newman told ABC Radio Brisbane the mine had regular inspections, and his department had been in contact with them in the past month.

When asked if there were any safety concerns at that point he said: “There were”.

“As in all inspections undertaken at mine sites, whenever you bring a fresh pair of eyes to an operation there are always either recommendations for improvements in certain aspects of the mine, or a directive in terms of the mine taking particular action.”

Mr Newman was reluctant to say whether the safety concerns were the cause of the explosion.

“They are monitoring the gas environment underground,” he said.

“Until such time that the monitoring and analysis of gas readings determines that there is a safe environment for people to return underground, it’s premature for me to speculate what the nature and cause of this incident was,” he said.

Queensland Mines Minister Anthony Lynham said two mine inspectors had already been on site, with two more to arrive on Thursday.

Anglo American’s chief executive of its Metallurgical Coal business, Tyler Mitchelson, said the company wanted to ensure this type of incident never happened again.

“We are all devasted and we don’t yet understand what caused this incident,” he said.

“Once it is safe to return underground, we will commence an expert technical investigation to ensure we understand what has happened.”

Mines Minister Anthony Lynham said four mine investigators are at the scene, including the Deputy Chief Inspector of Mines.

“My primary concern is obviously for the injured workers and their families,” he said.

“Worker safety is in this government’s DNA and I expect a thorough independent investigation by the mine safety regulator.”

-AAP; additional reporting ABC