Three people - a married couple in their 60s and a 20-year-old man - have been killed and the young man's father is in a critical condition following a two-vehicle crash 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.

The married couple who were in one ute, and young man who was driving the other ute, died at the scene.

The father was in a critical condition at Middlemore Hospital.

A motorist who said he missed the accident by seconds described the deaths as "truly devastating".

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."

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 road had been reopened about 3am.

Emergency services were called to the south side of the bridge about 8.30pm.

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."

He said the service station was full at the time of the crash.

"It's been really busy here... and with the school holidays, there's a lot of people on the road."

Police units, ambulance, fire trucks and a rescue helicopter responded to the accident. The Serious Crash Unit was also there.

A Fire and Emergency spokesperson had confirmed four people were trapped.

A local resident told the Herald a rescue chopper landed at the scene about 9.20pm.

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."

The Kopu Bridge was replaced with two-lane bridge in 2011. It spans the Waihou River, near its emergence into the Firth of Thames and is 587m long.

Meanwhile, a man has been found dead near a motorbike on a Central Hawke's Bay farm.

Police and emergency services provided medical attention after the discovery at 5am this morning, but the man in his 50s died at the scene.

Police have referred to the incident as a sudden death.

The death is likely to be referred to WorkSafe and will be referred to the 
coroner.

And police are also this morning at a serious crash near Hanmer Springs in the South Island.

Emergency services were called to the crash on Percival Bridge on Hanmer Springs Road at 4.08am.

Two people have been taken to Christchurch Hospital, one with critical injuries and the other with serious injuries.

The road is closed and diversions are in place at River Rd and Jollies Pass Rd.

The Serious Crash Unit is at the scene.

A total of 125 people have died on the country's roads so far this year - 18 more than at this point last year.

These deaths have occurred in 109 fatal crashes - 12 more than last year.

Police were called at 6.30am yesterday morning to another two-car crash on SH2 just north of Dannevirke, where a motorist died.