The government is likely to appoint an independent expert to review New Zealand's foreign trust laws, says Prime Minister John Key.

Millions of leaked documents from a Panamanian law firm have shown how the world's elite set up tax shelters to hide wealth, including in New Zealand.

Transparency International New Zealand said for more than 15 years it had repeatedly warned the government about weaknesses in corporate ownership and trust legislation.

Photo: RNZ / Alexander Robertson

Last week Mr Key rejected any suggestion New Zealand was a tax haven, saying New Zealand had "full disclosure of information."

But in an apparent backdown Mr Key told RNZ's Morning Report he would take a proposal for a review to Cabinet today.

"It's highly likely, I think, that the government will ask an expert in this area to undertake an independent review - just for good order.

"Of course there may well (be), outside even of that independent review, in terms of disclosure ... it's possible that there'll be other learnings that come out of these papers.

Mr Key said he was not ruling out tighter rules on foreign trusts.

However he reiterated that the law had already been changed in 2006 amending disclosure provisions, the government had brought in anti-money laundering legislation and requirements for a shell company to have a New Zealand trustee.

"The advice that we have is that New Zealand's not a tax haven, it's compliant with OECD, in fact I think we're ranked in the top 20 of disclosure and good practice."

More than 12,000 offshore trusts are registered in New Zealand. An overseas trust set up in New Zealand with overseas assets but which does no business in this country and has no local income is tax-exempt.

Mr Key said there were legitimate reasons why people set up foreign trusts.

"There can be negative reasons and we obviously need to make sure we have the proper processes and procedures to ensure we don't get those.

"But there are also very legitimate reasons and New Zealand is a very good place in terms of being open, transparent."

Asked whether he had used an offshore tax account for investments, Mr Key said he had lived overseas so had had a superannuation fund in Singapore, the country he lived in at the time, but had never used tax shelter companies.

He had no intention of releasing his tax records. "We have very strong rules in New Zealand around pecuniary interest. I'm quite comfortable and very confident of my tax record. I use the best people, I don't use sheltering vehicles - I've never used those."

Latest developments on the fallout from the Panama Papers:

* Demonstrators in Malta's capital demanded the resignation of Prime Minister Joseph Muscat after the leaked documents said two of his political allies had offshore accounts.

* German Finance Minister Wolfgang Schaeuble gave details on moves to combat tax havens including creating company registers that list the names of company owners.

* British Prime Minister David Cameron took the unusual step on Sunday of publishing his tax records to try to end days of questions about his personal wealth caused by the mention of his late father's offshore fund.

*His accounts show Mr Cameron's mother gave him a £200,000 gift after his father's death which could potentially avoid inheritance tax.