A grainy video filmed on New Zealand's rugged west coast is the first 'credible' sighting of a father and his three children who vanished years ago and were believed to have lived in the wilderness ever since.

Tom Phillips, along with daughter Jayda, now 11, son Maverick, 9, and youngest daughter Ember, 8, disappeared from the New Zealand town of Marokopa in December 2021.

There had been 'hundreds' of sightings of Phillips reported to police since then, mostly unverified, but none involving the children.

The latest video is the most credible of the sightings, and the children's mother Catherine says she is delighted and relieved to see all three of her 'babies' alive.

The new footage shot on October 3 showed four figures in camouflage gear with heavy backpacks - an adult a few steps ahead of three children - as they walked in single file across rolling hills outside of their former home of Marokopa on the North Island.

The video, filmed by pig hunters, was handed to police, prompting a large search of farmland in the area this week which unfortunately failed to turn up any sign of the group.

The children's mother, who wants to be known only as Catherine, has seen the video.

'I'm so happy that they're all there,' she told the New Zealand Herald.

'I'm so relieved to see all three of my babies. They're all alive.'

Investigations are ongoing, with NZ Police Detective Inspector Andrew Saunders confirming the sighting was being treated as 'credible'.

'While nothing further of significance was located, investigators will now assess information gathered to determine any next steps,' he said.

'This is the first time all three of the children have been sighted, which is positive information, and we know it will be reassuring for the children's wider family.'

The father and his three young children first went missing on September 11, 2021.

Police and emergency services alongside hundreds of volunteers and locals spent days searching for the family after Phillips' ute was found below the high tide mark on Kiritehere Beach.

Some 18 days later they returned to the family farm with relatives revealing they had spent the time living in a tent in dense bushland.

However, months later they disappeared again, with the last sighting of the father and his three children on December 9, 2021.

Phillips failed to show up for a court appearance weeks later in January 2022 for a charge of causing wasteful deployment of police personnel and resources, and a warrant was issued for his arrest. 

He is now also wanted for questioning over an alleged armed robbery of a bank in Te Kuiti near Marokopa in September 2023.

The armed robbery prompted police to warn the public not to approach Phillips.

In June this year an $80,000 reward was offered for information that could locate the three children, however, this expired after eight weeks with no result despite more than 40 sightings deemed significant by officers. 

Inspector Saunders said police believe he has had help while on the run. 

'Immunity against prosecution will be considered for anyone who has committed an offence in assisting Tom Phillips, if they provide information or evidence which leads to the location and safe return of the children,' he said in June.

Catherine previously accused Mr Phillips of endangering and depriving the children.

'Ember is asthmatic as am I and she needs medical care that cannot be provided from the land,' she said.

'Many of you say that the children are fine and they are being well looked after.

'How do you know? Have you seen them? Or is it just bush talk?

'What Thomas is doing is not OK. It is not OK to divide and conquer, to isolate and control.

'It is child neglect, it is child abandonment, it is child abuse. My babies deserve better.'