Prime Minister John Key has revealed China's US$200 billion ($349 billion) sovereign-wealth fund has signalled its interest in a stake in NZ dairy giant Fonterra if it changes its capital structure.

China Investment Corp chief executive Lou Jiwei made the fund's interest in Fonterra, and other New Zealand assets, clear in a meeting with Key at the Boao Forum for Asia two weeks ago.

But Key stressed it was up to Fonterra's farmer shareholders to resolve the appropriate capital structure.

Sources told the Herald Key's preference would be for the NZ Superannuation Fund - rather than another nation's wealth fund - to take a stake in Fonterra.

The Prime Minister has made clear to Chinese investors that New Zealand would welcome increased investment particularly in greenfields or co-ventures.

Key also met a representative from the Canadian suitor for Auckland International Airport whose successful bid for a 40 per cent stake was overturned when Labour Cabinet ministers changed the overseas investment rules.

The Canadian meeting was described as "sensitive" by New Zealand officials - it was not on the formal diary Key's press advisers released to the Herald after he returned from Boao.

It is understood Mark Wiseman, the senior vice-president for private investments, fronted for the Canadian Pension Plan Investment Board.

Key said he made it clear to Wiseman his Government would issue distinct guidelines for foreign investors so they did not find themselves in the Canadians' position.

Also on the Prime Minister's dance card was a one-on-one meeting with former US President George W. Bush. Key said Bush was confident President Barack Obama's Administration would begin negotiations on the Trans Pacific Economic Partnership free trade agreement.

"He said 'Don't worry about Transpac - you'll get there'," said Key. "'It just takes a long time to bed in a new administration'."

In another meeting Key spoke to Hong Kong chief executive Donald Tsang.

Key expects the bilateral free trade deal between Hong Kong and New Zealand to be finished soon.