Work will start before Christmas on a controversial new stretch of motorway north of Auckland.

Photo: RNZ / Rebekah Parsons-King

The New Zealand Transport Agency has awarded a contract to Northern Express Group to finance, build, manage and maintain the Pūhoi to Warkworth road.

The estimated cost of the 18.5km-long motorway segment is $709 million.

Transport Minister Simon Bridges said it would increase economic growth in Northland and provide a more reliable link between the region and the upper North Island.

He said the new motorway was also critical to Auckland's success, because Warkworth was a key growth area for the city.

The Green Party said National was spending nearly a billion dollars to solve the problem of long-weekend holiday traffic north of Auckland, and the road would not even solve that.