WELLINGTON, Feb 14 (AFP) - The New Zealand government declared a national state of emergency on Tuesday (Feb 14) after a tropical storm lashed the North Island in what officials have described as an "unprecedented" natural disaster.

Minister for Emergency Management Kieran McAnulty signed the declaration as emergency services struggled to cope following heavy rain and strong winds that left tens of thousands of people without power.

"This is an unprecedented weather event that is having major impacts across much of the North Island," McAnulty said.

"We are all facing extensive floods, slips, damaged roads and infrastructure."

This is only the third time New Zealand has declared a state of emergency - the other two were the 2019 Christchurch attacks and 2020 COVID-19 pandemic.

Flood waters and landslides have cut off many settlements across the country including some near Auckland, New Zealand's largest city.

"This is a significant disaster with a real threat to lives of New Zealanders," warned McAnulty, adding that the national state of emergency will last seven days.

He said more rain and high winds were expected Tuesday hampering rescue efforts.

"The reports that came in overnight are deeply concerning," McAnulty told reporters.

"The emergency services are working night and day, but the unstable ground, flood waters and closed roads are making things hard."

The New Zealand Fire and Emergency services said a firefighter is missing and another is in a critical condition after a house collapsed in West Auckland.

"It's been a tough night for the North Island as a whole but it's been especially tough for fire and emergency," said Kerry Gregory, chief executive of the fire service.

McAnulty said his thoughts are with the two firefighters and urged New Zealanders "safety first" with some communities having been evacuated.

The freak weather grounded flights on Monday, but Air New Zealand have said they expect some services to resume on Tuesday afternoon.

Prime Minister Chris Hipkins has announced an aid package of NZ$11.5 million (US$7.25 million) to help recovery efforts, but McAnulty admitted the cost of the clean-up is set to spiral.

"The honest answer is that it's not going to be cheap, but that isn't what we are worried about right now," he added.

Auckland, home to 1.6 million, had already been struggling to mop up the damage after flooding claimed four lives at the end of January before the latest storm battered the city.

The national emergency management agency estimated 58,000 people across the North Island were without electricity on Monday as work continues to reconnect power.