New Zealand should be prepared for international criticism for its plan to open conservation land to mining, a tourism expert says.

Tourism Research Institute director Simon Milne said the plan was likely to be picked up on by international media, and tourist businesses should be prepared for the fallout.

"My concern is that people who have an eagle eye on our global image ... are going to say 'isn't this another case of something going on that doesn't match up with the national marketing campaign?"' he said.

"This is ... the juiciest of all ironies. Here you have got a country which is representing itself as 100 per cent pure and yet at the same time is talking about mining the conservation estate."

In November, Guardian columnist Fred Pearce - an author and environment journalist - said New Zealand was falsely trading on a positive environmental image.

"Within a day or so that (Guardian story) had generated ... 300 or 400 responses on their site," said Mr Milne.

Responding to a parliamentary question from Green Party co-leader Metiria Turei, Prime Minister and Tourism Minister John Key confirmed he hadn't sought advice regarding the potential impact of the mining proposals on the tourism industry.

That was fiscally irresponsible, said Ms Turei.

"He is willing to put the $21 billion-dollar-a-year tourism industry at risk without any advice, based on a back-of-the-envelope estimate from the mining industry," she said later.

Mr Key dismissed Ms Turei's concerns, saying new mines were "unlikely to turn back the 747s heading for New Zealand".

Tourism operators, however, said they feared the plan would be detrimental to their businesses.

Tourism Industry Association chief executive Tim Cossar said the majority in the industry were against the idea, and the controversy may already have damaged New Zealand's reputation.

However, some had pointed out that Doubtful Sound in the South Island may not have been opened for tourists without mining.