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.
