The underground continuous miner operation near Emerald, Queensland is still on alert after monitoring equipment detected the threat of an explosion on Tuesday.

Construction, Forestry, Mining and Energy Union representative Stuart Vaccaneo told International Longwall News that workers were withdrawn from the mine on Wednesday and would not be returned until a number of safety issues at the mine were resolved.

“Obviously there is an active spontaneous combustion event occurring in the mine in a worked out area of the mine that's inaccessible," he told ABC Online.

“There still are concerns about the levels of oxygen and other potentially explosive mixtures of gases that may be in the area."

In December 2006, Caledon Resources purchased a majority stake in Cook Colliery and took full operational control of the mine.

In 2007 the mine is projected to produce approximately 900,000 tonnes of coal, and based on existing reserves is expected to have a minimum 10-year mine life.