Miners had voiced concerns about gas levels at a Queensland coal mine before an underground blast left five men fighting for their lives, a union says.
The miners suffered horrific burns to their upper bodies and airways in Wednesday's blast at Anglo American's Grosvenor Coal Mine at Moranbah.
They were flown to Brisbane on separate planes and the mine remains closed - including to inspectors - until gas levels stabilise.
The Queensland government is considering establishing a board of inquiry with public hearings to determine what happened.
All five are now receiving specialist care in the Royal Brisbane and Women's Hospital. Source: AAP
Chief Inspector of Coal Mines Peter Newman said the company "informed us that there had been an ignition of gas on the long wall face".
"That is the extent of the information to date," he told ABC radio on Thursday.
He said mine inspectors had communication with the mine last month.
Asked if any safety issues were identified, Mr Newman said: "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 at the worst case a directive in terms of the mine taking particular action."
He did not directly answer when asked if Wednesday's incident was related to concerns previously raised with the mine.
Union boss Stephen Smyth, from the CFMEU, said workers at the mine had previously expressed concern about gas levels.
"This mine has a lot of gas issues. They certainly have trouble at times managing methane," he told ABC radio.
"There (have) been concerns by the workforce there around the gas levels."
Premier Annastacia Palaszczuk also refused to speculate on the cause.
Patients from a mine explosion being transported by RACQ Lifeflight Rescue Air Ambulance jets at a Moranbah airport. Source: RACQ LIFEFLIGHT RESCUE
She said Mines Minister Anthony Lynham was flying to Moranbah on Thursday to speak to officials about the incident.
"The mines have a duty of care to ensure their workers go to work safely and return home safely and this has not happened in this case," she told reporters.
"Our thoughts are with the families."
Mr Smyth said all underground workers at the Grosvenor mine were labour-hire or sub-contractors, and that compromised their ability to be vocal about safety concerns.
"Workers who are in labour-hire type roles are vulnerable because if they do speak up, they don't come back tomorrow," he said.
Four of the injured miners remain in a critical condition, with the fifth listed as serious.
They are all aged in their 40s and 50s and are being treated in the Royal Brisbane and Women's Hospital.
In a statement issued on Thursday, Anglo American said support was being offered to the injured miners and their families.
"We are all devastated and we don't yet understand what caused this incident. Once it is safe to return underground, we will commence an expert technical investigation to ensure we understand what has happened," said Tyler Mitchelson, CEO of Metallurgical Coal business.
Anglo American has evacuated the worksite, and all other employees have been accounted for.
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 "required urgent specialist care for their repatriation", he said. Those men were critical, with the fifth victim in serious condition.
The mine will remain closed on Thursday, as inspectors determine what happened.
The incident comes just months after a report found Queensland's mining sector is in the grip of a death cycle, with more lives are at risk without a safety overhaul.
The report reviewed the 47 deaths in the state's mines and quarries from 2000 to 2019, and made a series of recommendations after finding most of the deaths were entirely preventable.
