A serious two-vehicle crash on State Highway 1 near Whitby has closed all northbound lanes from Waitangirua Link Road, prompting major delays on Transmission Gully.
Emergency services were called to the scene around 3.25pm. Police have advised motorists to avoid the area and instead take the old State Highway route through Paremata and Plimmerton.
Southbound traffic is restricted to one lane, and congestion is expected throughout the afternoon.
One person sustained critical injuries and is being airlifted to hospital. The Serious Crash Unit has been notified and is investigating the cause of the incident.