For the next five weeks Auckland drivers will have restricted overnight access on the Northwestern Motorway (State Highway 16) because of roadworks, the NZ Transport Agency says.

The first set of closures will start on Sunday, when the NZTA starts closing off some of the causeway lanes between 9pm and 5am.

While lanes are closed, a series of geo-technical investigations will be conducted at different locations between the Te Atatu and Great North Road interchanges.

The NZTA's acting State Highways Manager for Auckland and Northland, Steve Mutton, said drivers would need to take extra care and reduce speed.