There were no injuries reported.
Waka Kotahi notified travellers of the crash south of the Newlands southbound onramp, shortly before 7am.
“Delays of up to 60 minutes are expected along this route. Tow trucks are currently on site removing vehicles,” the agency said on social media.
At 7.15am, traffic was queued back to the Transmission Gully/SH59 interchange. The interchange and Newlands offramp are about 8km apart.
“Road users are advised to expect delays and allow additional time for travel.”
As of 8.05am, the lanes had been cleared, but delays are expected to continue.
A video sent by a motorist showed at least six cars apparently involved in the crash.One Facebook user described the traffic as a “carpark” from Transmission Gully.
Another commuter said the travel information screen in Otaki earlier said it would be nearly three hours to get from Porirua to Wellington.
Another said the Maps app gave them a nearly two-hour journey from Porirua to the central city.
A driver heading north commented they drove past standstill traffic heading south near Johnsonville to the Newlands shops.
“Nose to tail in righthand lane heading into city ... Will be huge delays,” they wrote.
It took one driver 45 minutes to get from Tawa to Churton Park, and only 10 minutes to turn around and get home.
“Traffic was building massively everywhere, even on the back roads,” the user commented.