Prime Minister Jacinda Ardern on her way out of an event in Hamilton.

The Prime Minister is refusing to comment on her deputy's involvement with covertly taken photographs of journalists investigating his party, despite promising a positive election campaign.

Deputy Prime Minister Winston Peters told Magic Talk on Tuesday that NZ First was involved in the surveillance-style photos of Stuff journalist Matt Shand and RNZ reporter Guyon Espiner meeting former NZ First president Lester Gray in Tauranga.

These photos ended up on right-wing political blog The BFD, which has close links to the now defunct blog Whale Oil which was at the centre of the so-called "dirty politics" furore in 2014.

ROBERT KITCHIN/STUFF Jacinda Ardern refused to comment on Winston Peters' involvement with covert photos of journalists.

"We took the photographs just to prove that's the behaviour going on," Peters said.

He later contradicted himself somewhat, telling media in a statement that the photo had not been planned.

KEVIN STENT/STUFF "We took the photographs just to prove that's the behaviour going on," Peters told Magic Talk on Thursday.

"A supporter did think it odd when they saw ex-president Lester Gray with Mr Epsiner so took a photo. Simple as that."

Labour was deeply critical of links between Whale Oil and the National Party in 2014 but prime minister Jacinda Ardern is now refusing to comment on the matter.

A spokesman said it was a matter for NZ First on Thursday night and again on Friday morning. The prime minister refused to answer direct questions put to her at an event in Hamilton.

Ardern committed Labour to a "positive factual robust campaign" last month at her caucus retreat.

National Party deputy leader Paula Bennett condemned Ardern's silence, saying she needed to front up with Peters and explain what had happened.

"He made a definitive statement yesterday that he was involved in something that is at best unethical and at worst cuts through our democracy. Both himself and the prime minister have questions they have to answer."

"Ignorance and burying her head is not leadership."

Bennett said it needed to be established who took the photos and what their connection was to Peters.

She also queried how they had known to take a photo of Shand, who was not photographed alongside Gray and is not as publicly recognisable as Espiner.

Paul Tolich of the E Tū Union, who represent journalists, slammed Peters over the matter.

"Mr Peters needs to apologise to the journalists and give a categorical assurance nothing like this will happen again."

"The sort of tactics undertaken by New Zealand First in photographing the journalists and then having the photograph posted on a right-wing political blog is chillingly similar to other examples of attacks on journalists as they go about their work in countries where the freedom of journalists is suppressed."

Tolich is also a member of the Labour Party's NZ council, it's top extra-parliamentary grouping.

Journalist Nicky Hager, who wrote the book Dirty Politics about Whale Oil in 2014, said Peters should know better as he had been a target of such blogs himself.

"It seems a really bad idea for NZ First to use an attack blog involving Cameron Slater as the way that they try to communicate through the media," Hager told Stuff.

"They should know better because they have been the target of the same people many times in unscrupulous ways."

Slater does not appear to directly run The BFD and suffered a stroke last year.

But the blog has acted as a successor to Whale Oil since that site was shuttered due to legal pressure.

The last post on Whale Oil pointed readers to the The BFD as a successor and the email address associated with the URL leads back to Whale Oil.

Green Party co-leader James Shaw issued a statement saying the party was focused on reforming the electoral system.

"As people know, the Green Party has a long standing position that our democracy needs to be more transparent and fair. The Green Party's view is that we need to review and reform our electoral system, including donations, and that's what we are focussed on."

