A three-vehicle crash has forced the closure of State Highway 1 at Taihape and motorists are being detoured.

One person has life-threatening injuries, and three others with less-serious injuries have been taken to hospital.

One witness told the Herald she had “never seen anything like it”, with traffic backed up from the scene.

Police were called to the crash near Rauma Rd about 1.10pm, a spokeswoman said.

Hato Hone St John said one person with critical injuries was flown to Whanganui Base Hospital. Another person with moderate injuries was taken to the same hospital by ambulance.

Two others, one moderately injured and another with minor injuries, were taken to Palmerston North Hospital.

St John sent two ambulances, two helicopters, two rapid response vehicles, two operation managers and a prime responder.

Police said: “The road is blocked and diversions are in place. The diversions are not suitable for trucks at this stage.

“Motorists are advised to avoid the area if possible and expect delays.”

The New Zealand Transport Agency said the road was closed at 2.40pm.

“All emergency services are on-site. Please avoid the area or consider delaying your journey.”

One woman told the Herald more than 60 trucks, utes, buses and other large vehicles heading north were waiting for the crash to be cleared.

“I counted maybe 60 trucks, mainly big logistic trucks, pulled over,” she said.

“We were being directed off the main road.

“I was just using Google Maps, and it changed where it says we should go now, and we can’t continue straight down the main highway.

“Everyone’s being directed down Mangaone Valley Rd.”