New Zealand First Leader Winston Peters says his party will review the way it handles its party donations after complaints about its donations was referred to the Police, then the Serious Fraud Office (SFO).

In a statement this afternoon, Peters said he welcomed the Electoral Commission referring the complaints to the Police.

"It confirms our prior view that only the police would have the powers to determine the issues involved."

Soon after Commission referred the matter to the Police, the Police referred it to the SFO.

"At this stage the SFO will consider if an offence has been committed, or otherwise, and it is not appropriate to make any comment on specific detail that prejudges their investigation," Peters said.

Peters has always denied any wrongdoing.

"New Zealand First's arrangements for collecting donations has been the same as other political parties. The New Zealand First Foundation is built upon the trust deed of the National Party," he said.

The statement continued: "This does not imply any impropriety but is intended to ensure the party, as with all parties, have robust arrangements."

In fact, he said Commission's statement today further underscores the importance of reviewing the donations regime.

The Commission said in a statement this morning: "Based on the information available, we have formed the view that the New Zealand First Foundation has received donations which should have been treated as party donations for the New Zealand First Party."

Peters said he had been advised that in all its dealings, the NZ First Foundation sought outside legal advice and does not believe it has breached the Electoral Act.

"At this stage, the SFO will consider if an offence has been committed, or otherwise, and it is not appropriate to make any comment on specific detail that prejudges their investigation."

Earlier today, it was announced NZ First will face a police investigation over failing to declare donations after complaints were made regarding donations to the NZ First Foundation.

"Based on the information available, we have formed the view that the New Zealand First Foundation has received donations which should have been treated as party donations for the New Zealand First Party," an Electoral Commission spokesperson said this afternoon.

In the Commission's view, the donations were not properly transmitted to the Party and not disclosed as required by the Electoral Act 1993.

The commission does not have the investigative power to form a view as to whether an offence have been committed.

Therefore, the matters have been referred to the Police.

The Police, according to the Commission, have the necessary powers to investigate the knowledge and intent of those involved in fundraising, donating, and reporting donations.

Late last year, Stuff reported the NZ First Foundation appeared to have hidden political donations worth almost half a million dollars between April 2017 and March this year.

Many of these apparent donations to the foundation do not appear on the party's electoral returns.

In recent weeks, RNZ has reported details of some of the donors to the foundation.

That included companies controlled by Sir Graeme Hart, with two donations of $14,995 being made on the same day. Three seperate donations totalling $36,000 were also made by entities connected to the Van Den Brink family, which has an estimated net worth of $110 million.

That figure is important, as it's just under the threshold at which the donor has to be officially declared.