One person is in a critical condition and another is trapped after two trucks and a car collided on State Highway 1 north of Wellsford.

One person with critical injuries has been taken to hospital by helicopter after being freed by fire crews from a vehicle.

A second person was still trapped in a truck shortly after noon and two more people had serious injuries, a police spokeswoman said.

Fire crews were working to free the second person.

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Two vehicles had rolled in the crash but it was not initially clear whether they were the trucks or not.

One helicopter landed at the crash site near Te Hana Nurseries by 11.38am and a second helicopter was on its way, said fire communications shift manager Jarron Philips.

The crash happened at about 10.48am and SH1 was blocked for about an hour and fifteen minutes north of Auckland.

NZTA warned road users to expect delays in the area.

SH1 is blocked and diversions are in place at the intersection of SH1 and SH16
and SH1 and Mangawhai Road.

Police advise motorists to avoid the area if possible and expect delays.

The Serious Crash Unit are attending.