At least two people are in a critical condition with life-threatening injuries after a passenger coach rolled with 29 people on board on a major Australian highway.

Emergency services were called to the intersection of Queensland's Bruce Highway and Rangemore Rd at Gumlu, in the Whitsundays region between Bowen and Ayr, about 4pm.

Two people were being treated for significant head injuries and multi-system trauma, with 27 more passengers assessed.

Eleven ambulances as well as two helicopters and a Royal Flying Doctor Service plane are already at the scene.

No other vehicles are believed to have been involved in the incident, with Queensland Ambulance Service confirming to AAP that three stable patients have left the scene.