About a dozen emergency services vehicles rushed to Queens Drive, in the suburb of Windsor, about 4pm today.
The crash happened in a 50kmh zone near an entrance to Queens Park.
In a statement about 7pm, Detective Inspector Stuart Harvey said police could now confirm that "a number of people" had died.
"Emergency services were called to the two-vehicle crash, involving a heavy motor vehicle and a motor vehicle, on Queens Drive just before 4pm.
"Sadly, multiple people died at the scene."
The exact number has not yet been released.
Queens Drive will remain closed between St Andrew St and King St overnight. The Serious Crash Unit has been advised.
A reporter at the scene said many police cars, St John vehicles and Fire and Emergency New Zealand (Fenz) appliances attended. Tents had been erected and cordons were in place.
A Fenz spokesman said they had responded to crash between a vehicle and a truck. There were people trapped when they arrived and the roof of the vehicle was cut off.
A St John spokeswoman said two ambulances and two management personnel attended.
They assessed one person, who did not need transportation to hospital. When asked about the condition of other vehicle occupants, she referred comment to police.
Det Insp Harvey said police would like to speak to anyone who witnessed the crash.
Anyone with information is asked to contact 105 quoting event number P050332364. Information can also be passed on anonymously through Crime Stoppers on 0800 555 111.
A nearby resident said he heard a big bang and went outside to look.
He saw a black four-wheel-drive which had been shunted sideways across the road by a concrete pump truck and the roof of the 4WD was caved in.
An off-duty emergency nurse arrived before St John and assisted at the scene.
The man, along with some others, stopped oncoming traffic.
There had been three men in the truck and it was clear they were visibly distressed. One was walking up and down the footpath while the others stayed in the cab.
The resident said he went back inside once police arrived. It was ‘‘quite obvious’’ they did not want bystanders around and it had started to rain.
While the rain had been on and off all day, he did not think it contributed to the crash.
Some ambulance and fire services had since left and the site was being cleaned up.
- By Oscar Francis, Ben Tomsett and ODT Online
