Enquiries are ongoing into the circumstances that led to a fatal crash.

Emergency services were called to the horrific scene at Piarere on State Highway 1 at 2pm on Wednesday after a bus load of foreign tourists and two other vehicles collided on a northbound passing lane.

The DNZ Travel bus was carrying 11 tourists and a driver.

Police said three other people were spread across two other vehicles, a black Mazda ute and a silver Mazda liftback car.

The driver's side of the bus was mangled and the impact caused major damage to the fronts of the other two vehicles, with debris strewn across the highway near the intersection with Paparamu Road.

One person died at the scene, two people were critically injured, and four others suffered serious injuries.

Hato Hone St John said 13 injured people were transported by road and air to Waikato, Rotorua, Tauranga and Auckland hospitals.

A Northern Rescue spokesperson said both Auckland Westpac Rescue Helicopters airlifted a man in his 40s and a teenager to Auckland City Hospital.

Police are now appealing for information to assist the investigation.

"Police would like to hear from anyone who was travelling on State Highway 1 between Hamilton and Tirau between 1pm and 2pm on Wednesday who may have dashcam footage, or who witnessed incidents of dangerous driving," said a police spokesperson in a statement today.

"At this time Police can confirm only that a vehicle crossed the centreline, colliding with other vehicles.

"All other details about the circumstances of the crash remain under investigation."

Anyone with information or dashcam footage can contact Police on 105 online quoting file number 241128/6729.