Auckland civil defence is warning the region will be pounded by as bad if not worse weather in coming hours.
Auckland Council head of emergency management operations Aaron Davis said people needed to prepare for the next onslaught of intense rain which was due to hit the region by 11am.
It is not expected to let up until 9pm and there are fears of further flooding and slip damage across the already saturated city.
As much rain - or even more - was forecast to fall across the region as had already fallen in the past day.
More than 150mm has fallen north of Auckland with the city recording around 100mm of rain.
The overnight deluge has left many parts of the region saturated with widespread road closures, houses threatening to topple into the sea and massive landslides.
Now worse is yet to come.
"We're going to get downpours that will get impact," said Davis.
"The worst of the weather is still ahead of us."
Davis said the rain was likely to lead to further flooding and slips. People were advised to stay home if possible.
"If you don't need to travel don't go out," he said.
Motorists were advised to avoid travelling through flooded roads.
Other measures to minimise damage were to unblock drains and help neighbours who may be struggling with flooding.
Weatherwatch head forecaster Philip Duncan said the heavy rain would fall mainly across the centre of the country as ex-tropical cyclone Debbie tracked through Cook Strait tonight.
All the North Island remains under a heavy rain warning while damaging gales are forecast to batter western regions of both islands this afternoon.