A farmer who heard a fatal two-car crash on Friday says he knew from just the sound that it was 'going to be a bad one”.

Police, emergency services and a rescue helicopter were called about 5.30pm on Friday to a two-car head-on collision on State Highway 29, near Matamata, that left three people dead.

It was the Waikato's third fatal crash in less than a week, and the farmer says all he heard was a 'huge bang” on the stretch between Te Poi and Hinuera.

'It was an awful, sickening sound,” says the man, who spoke on the condition of anonymity.

Waikato Police Senior Sergeant Andrew O'Reilly says the three people who died at the scene were the only ones involved in the crash, and police are making inquiries.

Locals say the stretch of road linking Hamilton and Tauranga is getting busier every year, especially on weekends, but it's not known for many accidents.

The farmer says he heard 'no skids, no brakes - just boom” following the crash on Friday night.

He had a quick look down the road but decided he did not want to go any further.

'There was just the sound, no skidding, just the impact, I knew it was bad just from the sound of it.

'It's a bloody tragedy.”

He says the volume of traffic on the road is 'huge”, especially on a Friday afternoon and weekends, but emergency services arrived at the scene quickly.

'They were here pretty fast, but it was obvious they couldn't do anything to save them.”

The section of road was closed overnight Friday while the Serious Crash Unit examined the scene, and was reopened early on Saturday.

Senior Sergeant O'Reilly says police are making enquiries into the crash and it's likely to be referred to the Coroner.

It is the third fatal crash in the Waikato in the past week.

Aucklander Deon Hadley, 33, died at the scene after his silver Audi collided head on with an ambulance on State Highway 1 near Cambridge about 3.45am on Wednesday.

The ambulance officer was critically injured and was flown to Waikato Hospital where she died later that afternoon.

Ōtorohanga icon Karam Haddad, 82, died when his car collided with a truck on State Highway 3, south of Kihikihi, about 12.30pm on Wednesday.

-Matthew Martin/Stuff.