In the aftermath of the fiery fatal truck vs car crash on Hamilton's Ulster Street on Sunday, police say "speed" is a major factor that is being investigated.

Two people died at the scene of the collision where a car ploughed into the side of a turning delivery truck in the early hours of Sunday morning.

Two people remained in ICU in a critical condition while all others transported to ED were discharged on Sunday, Waikato Hospital says.

'Every fatality is a tragedy,” says Hamilton City Area Commander Inspector Will Loughrin.

'It's still really early in the piece and we are working with a number of factors but one of the main things we are looking at is the speed the vehicle was travelling prior to impact.”

The crash site was on a lower speed, 50km/h stretch of road in the city central area.

'We've been speaking to a number of witnesses, collecting CCTV as well as our serious crash investigation unit examining the scene itself.”

Investigations are still underway as to whether other factors like alcohol were involved, says Loughrin.

Police were called to the five-person crash about 3.45am in Whitiora.

The vehicle, carrying the four occupants, was driving west down Ulster street before colliding with the truck, which was travelling towards the city centre, turning right into a Pak'nSave Mill St driveway.

Police pulled people from the wreck and performed CPR after the vehicle became pinned underneath the truck, bursting into flames.

A St John spokesperson says five patients were transported to Waikato Hospital.

Loughrin couldn't comment further on what speed the vehicle was travelling at the time but in the critical minutes after, Loughrin says it was fortunate that staff happened to be in the vicinity of the crash site.

The crash could have very much ended with 'four fatalities” had things been different.

'It took a real team effort from all emergency services to help those that were involved.”

It is unknown if those involved in the crash were local but a name release of the victims will be happening in due time, he says.

The safety features on the road and the role of the heavy vehicle would also be looked into during the investigation.

Katarina Robinson, 18, was staying in a nearby motel when she heard a very loud 'boom” and ran out to see what the commotion was.

'The front of the car was squashed under the truck, so the driver had to be speeding real fast.

'I saw police officers pull four people out of the car. One girl and three men.”

She says two men who looked around 23 - 30 years old were rushed to hospital.

Following the crash three officers were treated for smoke inhalation after pulling the occupants from the burning vehicle.

They were were continuing to be supported by staff.

'Every fatality involves grieving family and friends, one is always too many and this one is really tragic in itself.

'It's hard to put into the words their actions and bravery [police staff] in terms of a car on fire and to be able to remove two people from that vehicle and give them a fighting chance is heroic.”

Brett Henshaw, managing director of Fonterra Brands New Zealand, confirmed one of its franchisee's delivery trucks was involved in an incident in Hamilton early on Sunday morning.

Henshaw says the truck driver escaped without any serious physical injuries, but is 'obviously shaken” and their team sre co-operating with the police investigation.

'We are doing what we can to support him, as our number one priority is people's safety and well-being,” he says.

A Fire and Emergency NZ spokesperson confirmed two fire crews responded to the crash, and fire investigators were at the scene.

-Te Aorewa Rolleston/Stuff.