Tens of thousands of homes in New Zealand were without power and hundreds of flights were cancelled Monday as a tropical storm lashed the north of the country.

A state of emergency was declared in five regions on the North Island, covering almost one-third of New Zealand's entire population of 5.1 million.

Although the storm was downgraded from a cyclone before it made landfall, high winds and torrential rains have already toppled trees, damaged roads and downed power lines.

Wellington-based Prime Minister Chris Hipkins was among thousands stuck in the northern city of Auckland after the wild weather grounded flights.

"Things will get worse before they get better," Hipkins told New Zealanders in a press conference Monday, calling for them to "be prepared, stay inside if you can".

He said the government had considered declaring a national state of emergency for only the third time in the country's history -- but it was not yet necessary.

The government announced an aid package of 11.5 million New Zealand dollars ($7.25 million) to help recovery efforts.

Police said one person was missing aboard a boat, which issued a distress call early Monday near Great Barrier Island, north of Auckland.

Winds of up to 140 kilometres (87 miles) per hour battered the Northland region, while Auckland's harbour bridge was rocked by gusts of 110 kph.

About 58,000 people were without power on Monday afternoon, according to Roger Ball, head of the national emergency management agency.

Emergency management minister Kieran McAnulty said Monday would be a difficult day due to the "highly dangerous" combination of high winds and heavy rain.

McAnulty added that it was "unsafe" to try and repair the network while the dangerous weather continued.

Auckland, New Zealand's largest city and home to 1.6 million people, is still recovering after flash floods in late January forced thousands from their homes and resulted in four deaths.

"Many people haven't been able to catch a break," Hipkins said.

"The need in the community is significant. The effects of the weather events have compounded that."

Auckland mayor Wayne Brown said the next 24 hours would be "challenging".

The weather has created chaos on New Zealand's travel network with scheduled flights, trains and buses grinding to a halt.

National carrier Air New Zealand said it had so far cancelled 509 flights, but normal services were expected to resume Tuesday.

The airline said the travel plans of some 10,000 international customers had been disrupted.