The crash on the Southern Motorway (SH1) between the Ellerslie-Penrose and Mount Wellington interchanges has been cleared and all lanes are now open.

Traffic remains congested from Northcote, across the Auckland Harbour Bridge through to Ellerslie.

The NZ Transport Agency advises motorists that the evening peak will be extended and to delay your journey if you can to give the traffic a chance to clear.

Earlier, one person was trapped with severe injuries following the two car crash this afternoon.

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The crash happened on the southbound lanes between the Ellerslie-Penrose and Mount Wellington exits at around 3pm.

Motorists were asked to avoid the area if possible and be patient if caught in traffic.

The police serious crash unit will be investigating.

The Transport Agency said just before 4pm that traffic has banked right back to the harbour bridge "and is continuing to build."

Appealing to drivers to avoid the Southern Motorway's southbound carriageway, it estimated it is taking more than 80 minutes to reach Manukau from downtown Auckland.

It expects clearing the scene to take "some time", given the police serious crash unit's investigation of the pileup.