One initial theory is that there was an ignition of gas on the longwall face.
The injured workers were taken to the nearby Moranbah Hospital by ambulance services shortly after 3pm on Wednesday suffering severe upper body burns.
An Anglo American spokeswoman said the company could confirm an incident had occurred this afternoon at its Grosvenor mine.
"Five people have been injured and transported to hospital," she said.
"All of the injured people's families have been contacted.
"All remaining on site personnel have been accounted for. The mine is in the process of being evacuated and operations stopped. Emergency response is currently underway."
The spokeswoman said the Queensland Mines Inspectorate had been contacted and Anglo American was working to ensure the injured people have the best available medical care.
The Construction, Forestry, Mining and Energy Union has also sent its own inspectors to the site.
It said those inspectors would be investigating what appeared to be an ignition of gas on the longwall face.
CFMEU Mining and Energy Queensland District president Stephen Smyth said the immediate priority was taking care of affected workers.
"Our thoughts and prayers are with the injured workers and their families, and all the workers at Grosvenor affected by today's events," he said.
"The union will do everything possible to support a return to safe conditions at the mine and get to the bottom of what has occurred today.
"Explosions are the worst nightmare for underground coal miners.
"We will make sure no stone is left unturned."
The explosion is a huge setback for the Queensland mining industry, which has sought to wind back the number of fatalities and injuries in the state by safety raising awareness among government, industry and unions.