The conveyor belt moved approximately 300mm when a splice clamp was released.

The movement caused the conveyor lifters to topple over, near where the roller change was being carried out.

The belt was isolated at the time of the incident and the counterweight was on the deck.

The NSW Resources Regulator said there were no injuries.

"Safe systems of work for people dealing with plant or structures must include the isolation, dissipation of energy and control of all mechanical energy sources from plant or structures," it said.