A 12-vehicle pile-up blocked eastbound lanes on Auckland's Northwestern Motorway on Monday night and left a motorist with critical injuries.
A Waka Kotahi spokesperson said the crash before the Rosebank Rd on-ramp blocked the centre lanes.
A full motorway closure for city-bound traffic was in place.
At one point there was a lane of traffic going past the crash, but that was later shut off.
A detour had been in place with drivers told to exit at the Patiki Rd off-ramp, turn left onto Rosebank Rd and rejoin the motorway.
The motorway was closed for several hours.
The spokesperson said there was less traffic on Monday night due to the school holidays.
"Emergency services are onsite, please slow down through the area," he said last night.
"Expect delays and pass the scene with care."
A witness said a male was cut from a vehicle by firefighters.
About three or four vehicles stopped to help the driver, he said.
The driver had a neck brace on.
The motorway was "absolutely gridlocked" but the fast lane was open at the time and traffic had been moving slowly past the scene, he said.
Newstalk ZB caller Ian said he had been stuck in the traffic "for ages".
"We're moving really, really slow. There are cars for Africa here. It's bumper to bumper in every lane. If I heard [about the crash] on the radio earlier, I wouldn't have come this way."
A St John ambulance spokeswoman confirmed one person was in a critical condition and had been transported to Auckland City Hospital.
A person with minor injuries was assessed at the scene but no hospital treatment was required. A St John rapid response unit responded.
A police spokesperson said officers responded to reports of a vehicle collision on the Northwestern Motorway at 6.15pm. The police serious crash unit attended.
"There appears to be multiple vehicles involved."
Police are seeking the offender's vehicle.