Auckland faces a high risk of coastal flooding tonight as a king tide combines with a sub tropical low heading over the city, a forecaster says.

Weatherwatch analyst Philip Duncan said high tide is expected to peak as the centre of the low crosses Auckland around 7pm.

The low could act as a "giant vacuum cleaner", lifting tide levels by up to a metre and causing flooding in coastal areas, he said.

He urged Aucklanders to take extra care around beach cliffs for the next week.

"The extra high tide is likely to erode the lower part of some cliff fronts tonight and this weekend - increasing the chance of dangerous rockfalls/slips. On top of that, more heavy rain is coming in to saturate the soil further."

Rain is expected to arrive in Auckland later this afternoon.

- nzherald.co.nz