New Zealand's North Island smashed by 'worst storm in 50 years'

New Zealand authorities have ordered mandatory evacuations and floods are threatening homes as Cyclone Cook arrives in the Bay of Plenty.

Heavy rain and severe gales have begun to hit the coast between Tauranga and Whakatane, with the storm making landfall after 6pm (local time) on Thursday.

• Ex-Cyclone Cook has made land in the North Island and is expected to bring winds of up to 150km; up to 50mm of rain is forecast to fall over some areas in the space of two hours
• Power has been cut to large parts of Whakatane, sections of Tauranga and a number of townships in the region; residents in Whakatane are being asked to conserve water
• The storm is now moving further south, causing flooding on SH1 in the Waikato, and numerous roads in the Hawke's Bay and Gisborne Gisborne regions
• More than 3000 homes across Hastings, Rotorua and Napier have lost electricity and Fire Service is receiving reports of wind damage to homes and lines in the Hawke's Bay
• Air New Zealand has cancelled all flights in and out of Rotorua, Tauranga, Hamilton, Blenheim, Nelson and Napier for the rest of the night

The Fire Service has already received dozen of calls about floods threatening homes in the Thames-Coromandel District, Matamata and Tauranga.

More than 1000 homes have lost power across the Bay of Plenty, according to Powerco, with Whakatane District Council reporting multiple trees have been downed.

Waves up to five metres could hit coastal areas later in the evening, and has prompted Civil Defence calls for people to leave low-lying and vulnerable coastal areas in the Bay of Plenty and the Coromandel Peninsula.

Winds could reach 150km/h, according to the MetService.

The storm is expected to move south overnight, reaching Wellington or the Wairarapa early on Friday.

The weather has also disrupted flights across the country, with Air New Zealand suspending all flights in and out of Tauranga.

Wellington airport has also been affected by the weather.

Fears Auckland would be hit by strong winds have been downgraded.

A state of emergency has been declared in the Bay of Plenty and Thames-Coromandel regions, which are still suffering from the aftermath of ex-tropical cyclone Debbie.

Metservice warned the storm could be the most intense since ex-Cyclone Giselle in 1968, which swept a ferry onto rocks in Wellington Harbour, killing 53 people.

Cyclone Cook on Monday dumped heavy rain on New Caledonia, where four people were hurt when a tree fell on their car and power supplies were disrupted. Damage, however, was limited.

"This is a very significant event and is likely to produce widespread flooding, (land)slips and wind damage, including to powerlines, and may even lift roofs and bring down large trees," Metservice said.

The New Zealand Transport Agency urged motorists to stay off the roads if possible, saying conditions would be hazardous.

Air New Zealand cancelled all flights from Rotorua, Napier, Hamilton and Tauranga in the North Island, and said it expected disruptions at Nelson and Blenheim in the South Island.