Jacinda Ardern says she won't stand Deputy PM Winston Peters down amid SFO probe

Prime Minister Jacinda Ardern says her deputy, Winston Peters, deserves "natural justice" and she will not stand him down as the Serious Fraud Office (SFO) probes the mysterious NZ First Foundation.

This is despite both National and ACT calling for Ardern to strip Peters of his ministerial portfolios as the SFO conducts its investigation.

This morning, the office confirmed it was investigating the NZ First Foundation after the Electoral Commission said last week its donations were "not properly transmitted to the Party and not disclosed as required by the Electoral Act".

Briefly speaking to reporters before going into the House this afternoon, Peters said he was not concerned about the investigation.

"We welcome it," he said.

"We want the truth to be out there, not a whole lot of false allegations."

He said he would not be standing down while the investigation took place.

Peters has always maintained that both he, and NZ First, were in the clear over any allegations of wrongdoing.

In 2008, Peters stepped aside as Foreign Affairs Minister amid an SFO investigation into party donations.

But Peters told reporters today the situation was different.

"They [the SFO at the time] said they were investigating me – I stood aside and was cleared by three official bodies."

The SFO's statement today said it was commencing an investigation in relation to the NZ First Foundation.

The timeline of the investigation is not clear.

Pushed for more details after Question Time this afternoon, Peters did not answer questions. Rather, he pulled out his phone and played Queen's "Radio Ga Ga" then said "that's you guys" before leaving the press pack.

Speaking to media, Ardern said she wouldn't comment on the matter until the SFO had finished its investigation.

Asked if she would stand Peters down, she said she was awaiting the outcome of the SFO investigation.

"In my mind, we need to apply natural justice here. I am awaiting the outcome of the SFO's investigation and that's the right thing to do."

She said she would not get into hypotheticals about what she would do if the SFO found any wrongdoing.

Peters had not offered to stand down, Ardern confirmed.

National's deputy leader Paula Bennett said this was not good enough and Ardern needed to sack Peters immediately.

"I think that he [Peters] should do what he did many years ago and offer up his resignation in the role of Deputy Prime Minister.

"But what we are seeing quite clearly, is actually the highest ethics are not being upheld within her Cabinet – she needs to take some responsibility for that."

She said it would be "very serious" for Peters if the SFO did bring charges against NZ First.