Two separate crashes involving multiple vehicles are causing long delays on Auckland's Northern Motorway early this morning.

A crash just before 7am on State Highway 1, citybound, has been quickly cleared but motorists are being warned to expect delays through Silverdale as a result.

There continues to be delays from Oteha Valley Rd after a multiple-vehicle crash just after the Upper Harbour Highway on-ramp.

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The collision happened about 6.30am and half an hour later, authorities were still working to clear the area.

"Only one lane available citybound past this crash scene,'' the NZ Transport Agency said.

"Consider delaying your journey or use Tristram Ave or Northcote on-ramps citybound if possible.''

Road cameras show at least three vehicles - including a van - blocking the middle lanes.

Congestion is building in the area as a result of the crash and people are being warned to expect long delays this morning.

"Pass with extra care...consider delaying your journey,'' NZTA said.

AUCKLAND HARBOUR BRIDGE:

Drivers heading north on the Auckland Harbour Bridge also face delays after a crash just before 7.30am.

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The NZTA said the collision is blocking the middle northbound lane and people should expect delays through St Marys Bay.

In other parts of the city, there is heavy traffic on the Southern Motorway (SH1) northbound through Papakura and Manurewa, as of 7.30am.

Congestion is considered moderate-to-heavy from East Tāmaki Rd through to Greenlane.

Traffic heading south, however, is flowing well.

Those driving into the city from West Auckland on the Northwestern Motorway can expect heavy congestion from Hobsonville through to Royal Rd and again from Te Atatu Rd through to St Lukes.

Congestion is moderate through Great North Rd, while northbound traffic on this motorway is smooth.

On the Southwestern Motorway (SH20), there is heavy traffic from Hillsborough through to Maioro St. An earlier crash on the centre median lane after the Queenstown Rd on-ramp has been cleared.

Meanwhile, moderate-to-heavy traffic can be expected from Lambie Dr through to Massey Road at the moment.

Those on the Upper Harbour Motorway (SH18) are in for similar conditions from Albany Highway through to Paul Matthews Rd; while westbound traffic is fine.