UPDATED 8.42PM: North and southbound lanes of State Highway One north of Auckland near Puhoi are open after being closed most of the day.

Speed restrictions of 30 kilometers an hour are in place, as the road remains slippery after tens of thousands of litres of milk fat flooded the road this morning.

Firefighters north of Auckland had a difficult task releasing a driver pinned between the cab and trailer of his milk tanker, which had rolled just before 5am.

More than 20 firefighters from Warkworth and Silverdale crews worked for more than two hours to free the man, who is now in a stable condition at Auckland Hospital.

Warkworth Chief Fire Officer Ian Davies said the man's arm had busted through the back window and was trapped between the cab of the vehicle and the tank behind it.

"We used spreaders, cutters, airbags, you name it, we used it. He was quite badly trapped - his foot, pelvis and his arm - so we had to do three scenarios to get him released from each one."

He said they're thankful he's okay.

"Our concerns go to him and the family and hopefully he'll recover and be okay. And everybody else driving home today, drive safely and try not to make us do anymore work for the day."

The man is now in a stable condition in Auckland Hospital.

The spilt milk congealed and the road was closed for much of the day, with diversions in place onto Highway 16.

Two high-powered water blasters were used to clear the greasy surface and experts were brought in to find chemicals that could clear the solidified milk.

Police said it looked like an ice-skating rink, and they are asking drivers to be patient.