"After weeks of the Prime Minister claiming our foreign trust industry has full disclosure of ownership and saying for years that there is no need for a register of foreign land sales, Judith Collins has told the world that National is investigating changes to stop people hiding their assets," he said.
Mr Key would not be drawn on whether the Government was considering a public register as a direct result of the Panama Papers.
He said that it was raised in a special OECD meeting of tax officials in Paris last month, and was being pushed by British Prime Minister David Cameron.
"If the world adopts a register, New Zealand will certainly be fulfilling its obligations and will happily be doing so."
The Inland Revenue Department has this week been reviewing the Panama Papers database published online by the International Consortium of Investigative Journalists.
It had found 200 New Zealand entities which were linked to controversial law firm Mossack Fonseca, all of which had been disclosed to IRD.
"In a way, New Zealanders can take confidence that the tax system is working," Mr Key said.
"It didn't throw up -- from what we can see so far -- a raft of New Zealanders trying to hide money offshore.
"It doesn't mean that there aren't learnings that come out of the papers and changes that might need to happen."