Hundreds of sheep were killed in a truck fire on the Mitchell Highway early Saturday.

The animals were being transported by road train travelling along the Mitchell Hwy north of Nyngan, when the truck caught fire about 12.50am.

The blaze was extinguished by NSW Fire and Rescue firefighters however an estimated 200 sheep aboard the road train were killed in the blaze.

The 32-year-old truck driver was uninjured, and investigations into the fire are continuing.