A Hamilton resident has described his shock at seeing a car "ripped in half" after a crash which killed four people on Friday night.
The victims -- aged 19, 20, 24 and 28 -- were travelling in a white Nissan Skyline which took a corner on the wrong side of the road and lost control, crashing into a van near Hamilton International Airport just before 10pm.
The van driver was taken to Waikato Hospital with serious injuries, including fractured legs.
Steve Hartland, who lives nearby, said he was watching television when he "heard a couple of cars screaming down the road".
"When I got out there, there was a Skyline ripped in half. The front half was on the road, the second half was up against the airport security fence."
Mr Hartland says after the initial bang, he heard another vehicle speed off, as if the two cars might have been racing. It's not unusual for drivers to speed in the area at night, he says.
"I'm waiting for the day that one comes through my place -- it's not if, it's when."
Inspector Freda Grace said police had heard about the possibility of a second vehicle, and were investigating it.
"We have witnesses that have indicated that potentially there was another vehicle involved -- and we are continuing with our inquiries to establish exactly what part to play that vehicle had in it."
She said the crash was "very, very disappointing" and a tragedy for both the families of the victims and the wider Waikato community.
Inspector Grace said police are also investigating whether street racing and alcohol consumption contributed to the crash -- but said speeding was the thing police were "really concerned" about.
"We're working very closely with the New Zealand Transport Agency and the regional council around speed management for the Waikato District," she said.
"It's just a matter of physics -- the faster you go the bigger the mess -- so speed is very important to us. We're working hard with our partner agencies to achieve some better outcomes for this district in that area."
Police are asking anybody who may have seen the Skyline in Te Awamutu prior to the incident -- around 9:30pm -- to contact them immediately on (07) 872 0100.
They say the Nissan was seen travelling with a second vehicle, a small white hatchback with possibly tinted windows. Both vehicles were reportedly seen together in the Ohaupo village just before the crash.
It brings the total number of fatal crashes in Waikato this year to 25; compared to the 20 recorded at the same time last year.
Thirty-four people have been killed as a result of these incidents.
Police have called the toll a tragedy and took to Facebook asking drivers to slow down and take extra care.
"While we have many who drive safety and to the rules each day, and while we applaud these drivers, the crashes and loss of life clearly demonstrate that when a mistake is made, the consequences are devastating and far reaching."