Midway through the day, the worker attempted to refuel the unit.
The NSW Resources Regulator said a fire erupted during the process.
"The worker was seen rolling on the ground before getting up and removing their jacket," he said.
"The worker was treated on site before being transferred to hospital."
The regulator said alternate power sources such as diesel or battery power must be considered before using petrol is considered.
"Where it is determined petrol-powered equipment cannot be substituted, mine operators must assess the risk of using petrol on site," it said.
"Controls must be implemented to manage the risk of refuelling. As a minimum, engines must be stopped and allowed to cool before petrol refuelling starts."