Police are warning motorists of lengthy delays after a heavy vehicle crash south of Twizel this afternoon.

The crash was reported about 12.25pm today on the Twizel-Omarama Rd (State Highway 8), near High Country Salmon.

A police spokeswoman said there were no injuries reported.

However, the road was fully blocked by the truck. Motorists were advised to take alternative routes or expect "lengthy" delays.

A Fire and Emergency NZ spokesman said the crash was between a truck and a four-wheel drive vehicle.

No one was trapped, he said.

Rescue tenders from Twizel and Omarama and a pump appliance from Otematata had attended.

A Hato Hone St John spokeswoman said one ambulance and Prime responder attended the crash.

Two people were assessed at the scene but were uninjured.