All lanes are now clear at the site of this morning's serious crash on the Southern Motorway but motorists are still being warned to expect delays from the Harbour Bridge.

The crash was on the southbound approach to the Newmarket Viaduct where one car with a heavily crumpled front appeared to have gone into the central barrier. A second car was on its side in the outside of four lanes.

Multiple emergency vehicles attended the scene. Some parked in a funnel-style formation to restrict the flow of traffic through the scene.

Fire Service northern communications shift manager Jarron Philips said four vehicles were involved in the incident.

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Three people were treated for minor injuries at the scene by ambulance staff, he said. Rubberneckers also caused delays to northbound traffic, the Transport Agency said.

NewstalkZB timesaver traffic is warning commuters using the motorway system to be prepared for a long, slow ride to work.

It is taking more than an hour and a half to travel from Drury to the city, almost an hour on the Northern Motorway from Oteha to the city and one hour and 19 minutes from Westgate to the city on the Northwestern motorway.