UPDATED 5.04PM: Waikato police say they're investigating whether two cars were racing each other before a crash on a straight stretch of road near Hamilton that left four people dead and one in hospital.

Around 10 last night a Nissan Skyline collided with a van in the southbound lane on State Highway Three, near the airport.

It's thought a third vehicle was involved - but police say they're not sure yet in what capacity.

The four people in the Skyline died on impact, while the driver of the van is in Waikato Hospital with a number of serious injuries to his legs.

At a press conference this afternoon in Hamilton Inspector Freda Grace said speed was definitely a factor.

"This is an absolute tragedy, and an avoidable tragedy."

A witness to the crash believed two of the cars were racing each other.

Police confirmed all victims were from the Waipa District - which includes Te Awamutu township.

There were three men aged 28, 20 and 19 in the car as well as a 24-year-old woman.

Grace also confirmed there was an earlier incident at a petrol station in Te Awamutu involving the driver of the Nissan Skyline and a vehicle which was first to the scene of the crash. However, police were currently investigating what happened and wouldn’t elaborate.

“We do understand that one of the vehicles was at the petrol station, yes and that somebody else that turned up to the scene had seen that car at the petrol station as well.”

Witness Steve Hartland said the crash happened right in front of him, and afterwards he spoke to a driver who'd been following the cars.

"The guy in the ute was telling me as he was coming down the hill, he was doing 110-120, but the Subaru was passing him, and then the Skyline was passing him again.

"So even if his car was coming up that road, nobody would have been able to get through.

“I could actually hear going nuts coming down the road - that’s what got my attention so I went up to have a look. The skyline was on the wrong side of the road and he slid sideways and collected the van.”

Hartland said the impact of the crash left the skyline ripped in half with the back half wedged into the airport’s security fence and the other half left on the road.

Mike Aldridge posted on Facebook a dramatic account of the moments following the collision.

“Saw this last night only a couple of minutes after it had happened.

“There was nothing left of the Skyline. Just a cloud of dust hanging gently in the air and an eerie silence.”

He described how one man “in a bit of a daze” was walking along the growing tailback telling drivers there'd been an accident.

“Such a tragedy for the families and friends involved,” he wrote.

Multiple fire crews with a dozen firefighters were called to the scene, and had to work to free the trapped occupants.

All four deceased died at the scene.

Police will investigate the cause of the crash.

"This is a tragic and distressing time for the families of the deceased," police said in a statement.

"We urge all drivers to take care on the roads. Please drive carefully and to the conditions."

Speed and alcohol are also suspected as factors in the crash.