A man in his 20s is being airlifted to hospital after he was crushed by an excavator bucket in a rural Queensland property outside of Toowoomba.

He is being taken to Princess Alexndra Hospital with serious head injuries after the incident about 4pm on Wednesday.

An RACQ LifeFlight Rescue spokeswoman said the man was helping to clear out a dam with heavy machinery, when the bobcat became bogged in mud.

"He was assisting with the removal of the trapped bobcat and was standing next to the excavator when its bucket dropped down and crushed him," she said.