The crash happened at the Kopu Bridge in Coromandel on Friday morning, bringing road toll so far in 2018 to 125.
One of the utes involved in a crash where three people died had been reported stolen.
Three people - a married couple in their 60s and a 20-year-old man - were killed and the young man's father is in hospital following a two-vehicle collision at the Kopu Bridge in Coromandel.
The bridge, near Thames, was closed in both directions overnight following the collision between two utes about 8.30pm.
Police have confirmed one of the utes was part of an Auckland purchase that went wrong, and was reported stolen.
The married couple, from the Thames area, who were in one ute, and a young man who was driving the other ute, died at the scene.
Karl Smith said he had pulled to the side of the road on the west side of the bridge to make a quick, 14-second phone call.
"This was less than one minute before the crash," he wrote on Facebook. "I then pulled out near the front of the halted traffic when I found out this happened.
"If I didn't pull over, I might have ended up as part of the collision. Really scary to think of...
"My thoughts and prayers go towards the friends and relatives of the three killed and the one injured. Truly devastating."
Three people - a married couple in their 60s and a 20-year-old man - were killed in the Kopu Bridge crash in Coromandel. Image / Newshub
Thames-Coromandel mayor Sandra Goudie lives on the hill above Kopu and saw the aftermath of the incident unfold.
She said when she saw the helicopter land for a crash so close to the hospital she knew the crash must have been serious.
Calling it a "tragedy all round", Goudie said she was now waiting to find out whether she knew anyone involved.
"It's just awful," she said.
"I'm just waiting to hear who the people are, because if they're from the area I'm dreading to know who that might be.
Police said there were two people in each vehicle.
Waikato Senior Sergeant Simon Cherry said the married couple were driving a Toyota ute and the father and son were in a Mazda ute.
The crash is being investigated by the Serious Crash Unit but initial indications suggest the car driven by the 20-year-old crossed the centre line and collided with the other car.
The road had been reopened about 3am.
Eighteen Fire and Emergency NZ firefighters from Thames and Ngatea attended the crash.
Thames Fire Brigade senior station officer Shane Bromley was at the scene, where he said they had to cut the solo survivor out of their vehicle.
The survivor was transported to hospital by helicopter.
Contractors repair the road at the scene on State Highway 25 just off the southern end of Kopu bridge, Thames, where 3 people killed in a serious accident. Photo / Brett Phibbs
Bromley could not confirm the nature of the patient's injuries - he said it was common for crews to "switch off" in a sense, to better cope with what they were seeing.
"I couldn't even tell you what colour the vehicles were - that's the way these incidents are."
Kopu Mobil station worker Neil said there'd been a flurry of police activity.
"Three, four cop cars came flying past, and then probably three fire trucks.
"They were in a hurry, it seemed very dramatic, so something bad's happened."
A local resident told the Herald a rescue chopper landed at the scene about 9.20pm.
Auckland Westpac Rescue Helicopter crew chief Mark Cannell said they were initially told there were four critically-injured people, trapped in the vehicles.
"When we got there we saw extensive damage. We uplifted the male survivor from one of the vehicles.
"He was initally critical, with multiple injuries, but was in a serious condition by the time we got to Middlemore Hospital."
Motorists were asked to avoid the area with diversions in place overnight.
The bridge forms part of State Highway 25, connecting Thames to the Hauraki district.
In a statement, NZTA said: "Due to a crash on the Western side of the Thames Bridge, the road is closed. Emergency services are on site. Please delay your journey or use an alternative route."
