Hundreds of sheep have died after a truck crashed on a highway in regional NSW.

The truck crashed on the Oxley Hwy near Booloola Rd in Goolhi, west of Gunnedah, about 1am on Thursday.

Police say several hundred sheep died as a result of the crash.

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The male truck driver suffered non-life-threatening injuries and was taken to Tamworth Hospital.

It’s unclear at this stage what caused the crash.

The Oxley Highway is closed in both directions between Mullaley and Coonabarabran.

Those travelling eastbound should instead use the Newell Hwy or Kamilaroi Hwy to Boggabri, or Grain Valley Rd to get to Mullaley.

Motorists going westbound should use Grain Valley Rd to Boggabri or the Kamilaroi Hwy or Newell Hwy.

According to Transport for NSW the diversions will add 2.5 hours to the trip.

Anyone who witnessed the crash or has any information has been urged to come forward.