An off-duty doctor was among the first on the scene of a crash that seriously injured a truck driver and partially shut down State Highway 33 between Rotorua and Tauranga for most of today.

Part of the highway is partially blocked following the crash and is expected to be until early this evening.

Emergency services were notified at 8.57am of a serious crash involving a truck and a ute on State Highway 33 - Three Mile Hill - between Paengaroa and Sun Valley.

The truck is on its side and is blocking the road.

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Senior Sergeant Ian Campion said a man driving the truck was flown to Rotorua Hospital with serious injuries.

Campion said a doctor who had just finished his shift and was driving home was among the first on the scene and "assisted significantly at the scene".

The truck driver had been trapped inside his cab for at least 20 minutes, Campion said.

A man driving the ute was not hurt, he said.

A police spokeswoman said at 4.15pm diversions were still in place and the road was expected to remain partially blocked until early evening when the truck was removed.

She said the truck was carrying milk cartons and the vehicle was extensively damaged in the crash, causing the milk cartons to be strewn across the road.

Motorists are asked to avoid the area if at all possible.

Police said State Highway 36 was an option for motorists travelling between Rotorua and Tauranga.

Fire and Emergency New Zealand shift manager Jaron Philips said earlier firefighters from Maketu, Rotorua and Kawerau were heading to the "serious crash".

There were earlier reports a vehicle was on fire but the fire crews have since confirmed this was not the case.

A reporter on the Rotorua side of the crash said a truck was rolled against the bank and a car was smashed up against the bank on the other side of the road.

Traffic was backed up and had been turned around. A diversion was in place at Maniatutu Rd.

A reporter in Paengaroa said traffic was being diverted at Old Coach Rd in Paengaroa, although most cars were turning around and heading back towards Te Puke.

Traffic was backed up about 250m in the village, he said.