Thousands of homes in New Zealand were without power and flights were grounded Monday as a tropical storm lashed the north of the country.

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

Although the storm has weakened from its previous cyclone status, it has already toppled trees, damaged roads and downed power lines.

A state of emergency has been declared in five northern regions including Auckland.

Some 58,000 people in New Zealand's North Island are without power.

Officials warn it could take days to restore the network.

"As long as the weather continues to be as severe as it is, it's actually unsafe" to work on the network, McAnulty said.

New Zealand's largest city - home to 1.6 million people - is still recovering after flash floods last month caused four deaths and forced thousands from their homes.

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

McAnulty said the government is considering declaring a national state of emergency for only the third time in the country's history, "but we may not have to".

The weather also wreaked havoc on New Zealand's travel network, with flights, trains and bus schedules all badly affected.

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

The airline said 10,000 international customers were disrupted, with 6,500 left to be rebooked.