Aucklanders have been warned to expect delays as tractors and utes head south following a protest in the city centre.
A serious crash has also closed the northbound lane at Mangere's Coronation Rd and an incident involving a truck losing its bin near Mercer has delayed southbound travellers.
Waka Kotahi, New Zealand's Transport Agency, said traffic was "very heavy" on the southern motorway at 2pm and advised motorists to delay their journey or consider using State Highway 20 as an alternative route to Manukau.
At 2.30pm, Waka Kotahi confirmed southbound traffic was still moving slow from the city centre to Papakura. Motorists were advised to allow extra time for their journey.