Freak tides could flood parts of the Auckland motorway network tonight and tomorrow.

The New Zealand Transport Agency said the areas at most risk are the northwestern motorway causeway between Pt Chev and Avondale and the northern motorway southbound from Esmonde Rd to the Exmouth Rd footbridge.

Critical times will be high tides at 8pm tonight and 8am and 9pm tomorrow.

"We're on flood alert and have a number of measures in place to ensure the motorways at those points remain safe, but people will need to take extreme care over the next day or so,'' said agency spokesman Tommy Parker.


Average high tides in the Waitemata Harbour vary between 2.6 and 3 metres, but it is expected high tides over the next two days to vary between 3.4 and 3.6 metres.

The high tides coincide with a rain front accompanied by strong winds moving across the country. The front's low atmospheric pressure can increase tide levels.

"It's almost certain the northwestern cycleway adjacent to the motorway will be flooded - we are asking people to avoid using it 90 minutes either side of the high tides,'' Mr Parker said.

"Tidal water could also cover bus lanes or outer traffic lanes on the motorways.''

Roadside message boards will keep drivers informed. Response crews are on standby to close lanes and redirect traffic if necessary.

"We'll do everything we can to keep the motorways fully open and safe but the weather - particularly the wind - will be the critical factor over the next 36 hours,'' said Mr Parker.