There's limited access to Auckland's northern motorway (State Highway 1) from some on-ramps this morning so cyclists can use the Auckland Harbour Bridge.

Two lanes of the bridge are closed to cars until 9.45AM for the Bike the Bridge event.

The Shelly Beach Road off-ramp (exit 423) is also shut.

Access is restricted at the Constellation Drive interchange on the northern motorway (exit 414) and a short section of the Upper Harbour Highway (State Highway 18) until 8.00AM.

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The New Zealand Transport Agency (NZTA) says although the event is timed for when traffic volumes are light, the temporary changes mean people will have to drive with a lot of care and attention, as they will be sharing parts of Auckland's motorway network with hundreds of cyclists.

There is also some disruption to local roads at Curran Street, under the Harbour Bridge, and along the Dairy Flat Highway between Oteha Valley Road and The Avenue.

The Northern Busway is also closed.