Heavy rain has begun to hit New Zealand's North Island, ahead of what is being called the worst storm in generations.
New Zealanders have evacuated towns along the north coast, where severe weather warnings are in place.
(Stock Photo courtesy of 123rf)
The storm is due to make landfall from 19:00 local time (07:00GMT) over Bay of Plenty. Officials have warned of high waves, storm surges and landslides.
It is then expected to move to the South Island early on Friday.
It comes after severe floods caused by the remnants of Cyclone Debbie hit some parts of the country last week.
The storm - expected to bring torrential rain and winds gusting at up to 150km/h (93mph) - has been classified as an extra-tropical cyclone.
That means it has changed into a different kind of weather system on approach to New Zealand, but has not necessarily weakened or been downgraded, according to the New Zealand MetService.
Parts of New Zealand's North Island are now under a state of emergency, with residents in the low-lying parts of Coromandel, which has already seen landslips and closed roads, being told to leave immediately.
The BBC's Hywel Griffith says Bay of Plenty, which suffered flooding last week caused by the tail end of Cyclone Debbie, is expecting 300mm (11in) of rain to fall, which means some houses may be flooded again.
One local, Ian Jenkins, was fishing on Lake Taupo together with his wife when they saw a swirling storm approach across the water.
"It was very calm, hardly a breeze" when suddenly the weather began to change, he told the BBC.
Schools and businesses across the island have been shut early while residents in Auckland, which has already seen flooding, have been stocking up on emergency supplies.
The New Zealand military and emergency service teams are on standby. Flights across the country have either been delayed or cancelled, and national carrier Air New Zealand has suspended operations from Tauranga Airport in the North Island.
The cyclone formed around Vanuatu on Sunday and moved towards New Caledonia, bringing heavy rain and winds and causing cuts to power and water supplies. One man died in New Caledonia when he was trying to cross a river to a friend's home.
New Zealand weather officials say that Cyclone Cook will be the worst to hit the country since 1968.
They have also warned that it is a "really tightly packed cyclone" that will bring a "phenomenal" amount of rain and wind, reported The New Zealand Herald, compared to Cyclone Debbie which was more spread out.
Cyclone Debbie hit Australia at the end of March, before its remnants moved towards New Zealand.
It soaked New Zealand cities like Wellington and Auckland and caused the entire town of Edgecumbe to be evacuated.
Authorities are now worried about how Cyclone Cook will impact land that is already saturated from heavy rains.
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