New video footage is believed to be the first "genuine" sighting of a fugitive father and three children who mysteriously vanished nearly three years ago.

The footage, filmed on an isolated part of New Zealand's west coast is said to be the first "credible" of the four who are believed to be living off the land in the wilderness.

Tom Phillips, daughter Jayda, 11, son Maverick, nine, and youngest daughter Ember, eight, were last seen in the town of Marokop on the North Island in December 2021.

"hundreds" of potential sightings of Phillips have been reported to police since, with most unverified, and none, until now, also with his children.

NZ Police Detective Inspector Andrew Saunders said the video sighting was being treated as "credible".

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

"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."

John McOviney, grandfather of the cameraman, said his grandson got within ten metres of the group and asked the children who they were and what they were doing.

Mr McOviney told 1News: "He asked 'does anyone know you are here' and one of the children replied 'only you' and they carried on walking."

He said the adult had a long beard and was carrying a gun, so he did not want to "test that".

The children's mother named only as Catherine said she was delighted and relieved to see all three of her "babies' alive" after viewing the clip.

Shot on October 3, and filmed from above, it shows four people in camouflage clothes carrying what appear to be heavy backpacks.

There is a male adult leading the group, ahead of three children.

They walk in single file across the lower part of some hills not far outside of Marokopa.

Filmed by a pig hunter, it was handed to police, which launched a major search of the area this week, involving helicopters, but still no trace of them was found.

Last December was not the first time they went missing together.

There has a huge search operation earlier ion 2021 after Phillips' ute was found below the high tide mark on Kiritehere Beach.

They were not found, but 18 days later returned to the family farm.

The four had been living in a tent in bushland before tehir return.

On December 9, 2021, they went again and have not returned.

Due to the resources used in the search, Phillips was charged with causing wasteful deployment of police personnel and resources, with a warrant issued for his arrest after he failed to appear at court in January 2022.

Police want to locate them to check the welfare of the children and anyone with any information is urged to come forward.

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

The public has been warned not to approach him.

In June police put up an $80,000 reward for information that could locate the children, but it expired after eight weeks without success.

Inspector Saunders believes he has had help while on the run, but offered immunity to anyone who came forward in June.

He said: "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."