Traffic on Auckland's northwestern motorway may have to contend with more than other vehicles in the next few days, with the risk of flooding from exceptionally high tides in Auckland's Waitemata Harbour.

Parts of the northwestern motorway were very close to sea level and the New Zealand Transport Agency (NZTA) warned motorists today high tides of up to 3.5m, nearly half a metre higher than normal, would begin today and last until Saturday.

The high tides happened in Auckland every six to seven years.