Fresh images of human remains at NZ's Pike River

New Zealand police have discovered fresh evidence of human remains at Pike River Mine, 13 years after an explosion killed 29 workers at the site.

The bodies of the victims have never been recovered, with families petitioning authorities to explore the collapsed South Island mine.

In recent months, a borehole drilling program has allowed for images to be taken from the mine shafts.

Bernie Monk, the father of killed miner Michael Monk, said he had been shown images from where his son was believed to have been working during the November 2010 explosion.

"The pictures are ultra clear," Mr Monk told news outlet Stuff, describing clothing and equipment and what he believed was a body.

Police say pathologists have not been able to guarantee they are human remains.

Mr Monk has campaigned for the reopening of the mine and exploration, with the ultimate goal of returning the bodies to their families, all the while knowing it may not be possible.

Even these pictures are beyond what they have been told would be possible to find.

"I'm grateful to the police for what they are doing," he said.

"We were constantly told that there would be nothing to retrieve. Ashes to ashes, dust to dust. That's the most frustrating thing about it."

Jacinda Ardern's government green-lit a $NZ50 million mission ($A47 million) to re-enter the mine and gather information.

Images of human remains have been found in at least two other locations over the last 18 months.

Exploration is due to wrap up within weeks.

Police are engaged in the task to find evidence to be used in a possible criminal investigation.

The deaths of the 29 men - including Australians William Joynson and Joshua Ufer - in explosions due to a methane build-up, is New Zealand's worst workplace accident in a century.

Detective superintendent Darryl Sweeney said recent drilling from three boreholes "have resulted in images useful to the ongoing criminal investigation".

"While we can't say with any certainty that we've located human remains, we have shared what we've found as well as the pathologists' conclusions," he said.

"Our thoughts are with the families as they process this news."

Anna Osborne, who lost her husband Milton, said last year the campaign had been worth it.

"We fought for the re-entry of the mine's drift and for the first borehole project and now we are getting closer to justice," she said.