A serious crash in south Auckland has left a truck driver fighting for his life.

All five southbound lanes of the busy arterial are closed, with traffic being diverted via Redoubt Road.

Few details are known about the incident, though ambulance staff are on scene near Redoubt Road in Manukau, treating the truck's sole occupant.

A St John spokeswoman says they're still trying to establish the driver's condition.

The Serious Crash Unit will investigate the incident.

Police say the busy road should reopen in time for the evening rush.