An area flooded during heavy rainfall in Auckland. Reuters

New Zealand officials on Tuesday asked residents in flood-ravaged Auckland to prepare for the onslaught of another storm as residents start a clean-up following a series of floods and landslips across New Zealand's biggest city over the weekend.

Four people lost their lives in flash floods and landslides that hit Auckland over the last three days amid record downpours. A state of emergency is in place in Auckland and Northland, the country's northernmost region.

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With more rain on the way, Auckland has already been swamped with record levels in the past four days, and sodden ground and full rivers mean new rainfall brings increased risks of flooding and land slips.

Beaches around the city of 1.6 million are off limits due to contaminated water, several main roads remain closed, and all Auckland schools will remain shut until Feb. 7. Evacuation centres have been set up across the city.

Prime Minister Chris Hipkins speaks during a press conference. File photo

New Zealand weather information provider Metservice forecast another 12 to 24 hours of heavy rain across the country's north from Tuesday afternoon, with up to 120 millimetres (4.7 inches) expected in parts of Auckland.

"It's lines of heavy rain coming in bands ... we do expect impacts during the overnight periods. So (expect) slips, further flooding," MetService meteorologist Georgina Griffiths said during a televised media briefing.

Prime Minister Chris Hipkins said his government would accept his Australian counterpart Anthony Albanese's offer of help with the floods.

"Absolutely, if there are ways that the Australians can help, we will absolutely take up those offers of support," Hipkins said ahead of a trip to Australia next week, his first foreign trip since becoming the country's leader earlier this month in the wake of predecessor Jacinda Ardern's resignation.

Vehicles stranded in floodwaters in Auckland on Saturday. AP

Auckland Emergency Management controller Rachel Kelleher said Auckland's domestic airport was now running at full capacity, while Auckland International Airport was operating at near capacity and hoped to return to normal operations soon.

National carrier Air New Zealand said in a statement on Tuesday it had added additional services and increased seat capacity to help customers whose plans had been disrupted by the weather. Of the 9,000 passengers impacted by the weather, it had rebooked 7,800 as of Tuesday afternoon.

A portable building rests on a car after floodwaters shifted the structure in Auckland on Saturday. AP

Meanwhile the city council has designated 77 houses as uninhabitable and has prevented people from entering them. A further 318 properties were deemed at risk, with access restricted to certain areas for short periods.

The insurance industry expects the costs associated with the flood to top the NZ$97 million ($62.5 million) spent following 2021's floods on New Zealand's West Coast.

Reuters