More than three times April's normal rainfall is striking some parts of New Zealand in just 48 hours as the remenants of Cyclone Debbie cross the tasman.

Nowhere is this more evident than at Hunua Falls, where incredible footage has emerged showing the mass of water striking the country.

A thick band of rain is currently pounding Auckland and surrounding region, and isn't expected to ease until after 6pm tonight.

Metservice meteorologist Lisa Murray said those in the area would be seeing some thunder and lightning, as well as bouts of extremely heavy downpours.

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"This rain band is affecting Auckland, extending all the way up to Northland, and down almost as far as Hamilton.

Hunua Falls in January. Photo / Stu Fleming
Hunua Falls in January. Photo / Stu Fleming

"It's moving to the west, so it will ease off this evening.

"That's the characteristic of a system like this, it comes in bands.

"So there are more bands of rain that are due to come in later, as well."

A severe thunderstorm watch is in place for the Auckland region, and squally gusts of up to 110km/h are possible.

Whangaparoa has recorded 167.8mm over the last 24 hours, while Auckland Airport has recorded 82.4mm.

Auckland usually gets 91mm of rain for all of April.

"This is a significant event, by any standards," Murray said.

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About 19,000 properties in South Auckland are without power.

A Vector spokeswoman said the power cut was affecting Manukau, Wiri and Clendon.

Transpower technicians were working to establish the cause of it but it was too early to say when power would be restored.

Both the Manukau train station and the Manukau Mall are without power

Auckland Council head of emergency management operations Aaron Davis said further slip and flooding damage was possible across the saturated city.

"If you don't need to travel don't go out," he said.

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.

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.

This rain band is moving into the Bay of Plenty this evening and is expected to be severe overnight, easing off around dawn.

FLOODING: What you need to know

• The Whanganui River is expected to breach its banks, leading to evacuations from low-lying areas this afternoon

• A state of emergency has been declared in Whanganui and Rangitikei

• Cliff in Auckland's Kohimarama collapses onto units

• Houses hang on the edge of cliff on Auckland's North shore

• About 19,000 properties are without power in Papatoetoe, Manukau and Wiri

• Vector's outages map is also showing power cuts in Whangaparoa, Albany, Mairangi Bay and Rosebank

• The worst of the weather will hit Auckland until 9pm today, MetService says

• Fire services responding to dozens of flooding-related callouts

• A heavy rainfall warning applies to the entire North Island and the north and west of the South Island

• Some areas may get three times April's normal rainfall in just 48 hours

• Central North Islanders are being told to keep survival items nearby