Motorists are facing heavy delays heading north into Auckland following a crash on the Southern Motorway.

The crash has blocked a northbound lane on the motorway near the Mt Wellington off ramp, Waka Kotahi NZ Transport Agency said.

Emergency teams are at the site, but motorists are warned to expect delays and to pass the crash scene with care.

Traffic is banked back to the Highbrook Dr on ramp, Waka Kotahi says.