A person has been seriously injured in a crash that is causing rush hour traffic chaos on Auckland's north-western motorway this afternoon.

Emergency services are the scene of the car crash just before the Great North off-ramp.

A St John spokeswoman said one person suffered serious injuries and would be taken to Auckland City Hospital.

Four other people have minor injuries and are currently being looked at by staff at the scene.

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The accident happened at about 3.45pm.

Photo / Supplied
Photo / Supplied

Motorists are being urged to drive carefully and expect delays and emergency services work at the scene.

A witness said it appeared one vehicle had rear-ended another, and the two vehicles were now mangled together.

At least three fire trucks and an ambulance were on the scene.

Ambulance staff had prepared a stretcher as firefighters worked to cut an occupant out.

The witness said traffic was backed up as far as the city.