Two crashes on Auckland's motorway network are causing delays for motorists this morning.

A cyclist is seriously injured after a collision with a truck in Wainui Rd, Silverdale. The incident happened about 8.15am.

Wainui Rd Is closed between Silverdale St and Waterloo Rd. NZTA is urging motorists to use Millwater Pkwy to access Hibiscus Coast Highway.

The Serious Crash Unit is investigating and police are warning motorists to avoid the area.

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Meanwhile, a crash on Auckland's Northwestern Motorway has caused congestion for commuters on their way to work and school.

The crash on the citybound side blocked lane 2 after the link from the Waterview Tunnel.

The crash is now cleared but the incident is causing delays back to the tunnel.

Traffic is also heavy between Hobsonville Rd and Royal Rd and heavy between Te Atatu Rd and Western Springs.

Traffic for the northwestern westbound and southbound Waterview Tunnel is free flowing.

Heavy traffic is also being reported for southbound traffic on the Southwestern between Maioro St and Queenstown Rd and citybound traffic on the Southern Motorway is heavy between Drury and Takanini.