A spate of incidents plaguing Auckland's motorways and roads have been cleared but drivers heading home after work are in for long delays.

Traffic cameras show traffic is backed up on most routes out of the city after various breakdowns, a crash and a diesel spill.

The New Zealand Transport Agency earlier said there was "significant" delays on State Highway 1 southbound from the Johnstone Tunnel and Cowan Bay Rd, near Puhoi, after a serious crash earlier today.

Three people, including a child, were seriously injured at the Cowan Bay Rd intersection at midday. All were taken to hospital with non life threatening injuries and the Serious Crash Unit is investigating.

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A broken down bus has since been cleared after it was holding up traffic at the intersection of Esmonde Rd and Lake Rd in Takapuna; and a diesel spill on the Hibiscus Coast Highway, near Wainui Rd, was blocking the left eastbound lane but has also since been cleared and reopened.

Adding to congestion was another breakdown blocking the Southern Motorway at Spaghetti Junction, near the Upper Queen St overbridge. The crash has been cleared but drivers were warned to take extra care.

Earlier a crash was blocking the right southbound lane on the Southern Motorway shortly before East Tamaki. The crash was cleared at 3.30pm but delays were expected.

Traffic is backed up to Silverdale following the Hibiscus Coast Highway incident and NZTA traffic cameras show vehicles are bumper to bumper. NZTA said it was heavy between the northwestern motorway and Edmonde Rd, between Northcote and Rosedale roads, Tristram Ave and the Harbour Bridge, and Oteha Valley Rd and Constellation Dr.

Officials have also warned central Auckland drivers to be wary of heavy traffic near Mount Eden this evening, with the Black Caps set to play Australia at Eden Park at 7pm.

Meanwhile, a young boy is fighting for his life after being struck by a car at a Mission Bay carpark shortly after 1.30pm.

The child, believed to be under the age of five, was taken to Starship children's hospital.