Cyclone Gabrielle death toll at six in New Zealand

A man in his 60s was killed in floodwaters in the Gisborne region overnight, becoming the fifth victim of the storm.

Late on Thursday, Fire and Emergency NZ (FENZ) confirmed the death of a volunteer firefighter who was critically injured when a house collapsed earlier in the week.

The incident, in Muriwai on Auckland's west coast, also claimed the life of a second firefighter.

"All of Fire and Emergency will feel his loss, and my heart goes out to his family," FENZ chief executive Kerry Gregory told the NZ Herald.

Mr Hipkins said police still had "grave concerns" for others, with the number of reports made for uncontactable people more than doubling on Thursday.

"We do need to be prepared for the likelihood that there will be more fatalities," he said from Wellington.

The prime minister undertook a tour of Gisborne earlier on Thursday, describing damage as "traumatic".

More than 10,000 people have been dislocated by the cyclone, with thousands spending the night at civil defence centres in hard-hit regions such as Hawke's Bay.

Maik Beekmans, a resident of the Hawke's Bay town of Eskdale, told Radio NZ a woman was missing after failing to escape rising waters at his property on Tuesday.

Already, one fatality has been confirmed in Eskdale - a child who died in floodwaters.

Mr Beekmans' best friend Gareth and his girlfriend spent three weeks house-sitting the Eskdale property while he was on holiday, finding themselves in the path of the storm.

"They sought refuge on our bench-top in the kitchen and the water kept rising. He smashed his way through the ceiling," Mr Beekmans said.

"The water kept rising into the ceiling space they had to clamour onto the roof ... only Gareth made it.

"We think he lost his girlfriend that night ... she disappeared under the house and she's been missing and things aren't looking great."

Local media have detailed eyewitness reports of bodies in the region, which police are yet to confirm.

As Thursday afternoon, 3544 reports of uncontactable people have been made with police.

Police believe that number includes many double-ups and is largely due to telecommunications and power outages.

Mr Hipkins said all 450 rescue requests that had been logged with Fire and Emergency NZ had been completed.

"That's great news, and I'm sure it'll be a big relief to everyone across the country," he said.

Gabrielle formed in the Coral Sea last week, carrying category-two intensity out of the tropics to New Zealand, battering various North Island communities from Sunday to Wednesday.

There is major damage to infrastructure, including roads, rail and power lines in several regions.

Mr Hipkins said there were still more than 100,000 houses without power, including much of the key regional centre of Napier.

Transport Minister Michael Wood said there was an "immediate focus on those necessities of life where people need them".

More than 700 defence force personnel have joined the effort, with 70 police also re-stationing to the eastern regions where concerns are highest.

Food and water drops have taken place in towns that have lost road access, with the navy sending supplies from Auckland by sea.

Two dozen Australian rescue workers will join the effort later this week after responding to a request from Kiwi authorities.

In Gisborne, Mr Hipkins said he'd also seen "the very best of New Zealand as well".

"We've seen communities coming together, wrapping support around each other, looking after each other."