The company removed its workforce on February 20 as a safety precaution.

Underground conditions have since started to normalise at the mine due to the measures taken.

An Anglo American spokesperson said the rise in gas levels appeared in the goaf, which was an area behind the longwall that caved in behind the coal face after mining.

The spokesperson said it was believed that a coal heating issue or change in coal face pressure had led to rising gas levels.

“At the time of the incident, we had been mining through some particularly challenging geology and every precaution was being taken,” the Anglo American spokesperson said.

“The conclusions from the expert review of the incident will inform a comprehensive risk assessment prior to re-entry, which will require regulatory approval.

“The safety of our workforce remains our priority and we are keeping them closely informed.”

The company is now working with internal and external experts to assess the cause of the gas spike.

The Moranbah North coal mine is located near Anglo American’s Grosvenor coal mine, where a gas-related accident occurred last year and injured 15 workers.

Anglo American employs more than 600 people and holds an 88 per cent stake in the Moranbah North mine.