A car has careened off the side of State Highway 2 on the Remutaka Hill and overturned, with one person reportedly injured.
A police spokesperson told the Herald the car went off the road at 9.42am and the driver has been flown to hospital.
Waka Kotahi NZ Transport Agency is urging motorists to be patient as congestion eases on the road.
It was initially closed, then under stop/go management but has since reopened completely.
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MetService meteorologist Peter Little says the ranges were drenched with heavy rain overnight and low cloud is contributing to poor visibility.
He says the poor conditions will stick around for the rest of the day, and is urging motorists to be careful.
"Drive to the conditions – when roads are wet, people need to take that into account."