Auckland's Southern Motorway has been closed while police attend to an incident.

Auckland's southern motorway has reopened after being completely shut to traffic in both directions after a police incident on Friday.

Traffic was flowing freely on the motorway at 7pm on Friday night, following the incident.

A police spokeswoman said officers had concerns for the wellbeing of a young woman. The motorway was closed about 3.15pm and reopened about 5pm.

BROOKE BATH/FAIRFAX NZ A police officer on Auckland's southern motorway.

Inspector Ian Brooker said the woman had been detained and would be seen by medical professionals.

Initially the north and southbound lanes were closed from Newmarket to Gillies Ave, with the Gillies Ave on-ramp also blocked off.

"During this incident police have tried to ensure the movement of traffic continued and several lanes were reopened during this time as the situation allowed, however our priority was the safety of everyone and we thank motorists for their patience and understanding over the past few hours," Brooker said.

NZ TRANSPORT AGENCY Traffic camera footage at Greenlane showing northbound traffic backed up as a result of the incident.

Some lanes were reopened about 3.45pm, more at 4.20pm and all lanes were reopened by 5pm.

Update: The police incident on the Sthn Mwy is now clear. Expect significant congestion in both directions. ^LC https://t.co/2R39YZKApS — NZTA Akld & Nthlnd (@NZTAAkl) April 21, 2017

Police at the time told motorists to expect delays and said it was a "fluid situation".

BROOKE BATH/FAIRFAXNZ Traffic was stopped before Mountain Rd, and the motorway was completely closed from Newmarket to Gillies Ave.

"Our priority at this time is the safety of the young woman and motorists."

Update: Sthn Mwy BLOCKED N-Bnd at Khyber Pass. Traffic is congested from Princes St. S-Bnd 2 lanes are now open. Expect long delays ^LC pic.twitter.com/LNRX7w8R3u — NZTA Akld & Nthlnd (@NZTAAkl) April 21, 2017

The ensuing traffic chaos is expected to compound traffic woes ahead of the opening of the World Masters Games at Eden Park on Friday night.

Before that event Auckland Transport had warned city workers to leave early because of expected congestion around Mt Eden and Kingsland.

Auckland Transport spokesman James Ireland said people should think about walking or catching public transport if they were headed to the World Masters Games on Friday.

Event buses will be running from Quay St, next to Britomart, and additional Western Line trains have been added.

Travel on event buses and trains is free for participants.

