Thick fog is making the morning commute extra slow on Auckland's motorways as traffic builds and a crash adds to delays.

The NZ Transport Agency said emergency services remained at the scene of a crash on the Southwestern Motorway northbound after Hillsborough.

The crash had been cleared from the lanes but delays were expected.

NZTA has also warned motorists to take extra care on the motorways this morning due to heavy fog in places.

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At 7.15am traffic was heavy in patches on all of the citybound routes.

Northern Motorway

Citybound:

Moderate to heavy between Greville Rd and city side of Auckland Harbour Bridge.

Northbound: Normal flows.

Southern Motorway
Citybound: Heavy between Papakura and Takanini, then moderate to heavy in patches from Otara to Greenlane.

Southbound: Free flowing.

Northwestern Motorway
Citybound: Heavy patch between Hobsonville Rd and Lincoln Rd. Then heavy and building from Great North Rd.

Westbound: Free flowing.

Waterview Tunnel Southbound Free flowing.

Southwestern Motorway
Southbound:​ Slow just after Puhinui Rd. A crash after Hillsborough Rd has been cleared but is still causing delays. Heavy from Queenstown Rd.

Northbound: Free flowing.

Waterview Tunnel Northbound​ Free flowing.