The truck, carrying close to 500 sheep, crashed at around 9pm. Police are investigating the cause of the accident.

The driver escaped uninjured, however a large number of the sheep were killed during the crash or put down later by a veterinarian on the scene.

The practice of transporting sheep via road has been criticised by Animals Australia following the accident.

"We are concerned because it is something that is increasing, rollovers and accidents," Animals Australia executive director Glenys Oogjes told the Central Western Daily.

"We want to ensure livestock are transported for the shortest period of time possible, with the best trucks and the best drivers possible."

She said it was unacceptable livestock could be transported for up to a 48 hour period.

NSW Farmers' Association animal welfare committee member Peter Carter has defended the procedure of transporting livestock by road.

"It is not sensible not to transport them on the road," he said.

"It is not practical.

"The amount of transport that occurs over the years, accidents like this don't happen often."

He said there were a number of regulations under the Australian Animal Welfare Standards and Guidelines for the land transport of livestock, which was complied with the assistance of the RSPCA, that ensured animals are transported as humanely and safely as possible.

They include measures to reduce the amount of waste produced by the animals while they are in transit, and ensuring the livestock are not overcrowded.

Mr Carter said it was sad to see such a large number of sheep die in an unfortunate accident.

"No-one could have protected the animals in an accident like that," he said.