Any issues with the Trans Pacific Partnership Agreement (TPPA) are manageable and overall it's good for the country, Prime Minister John Key says.
More than 25,000 people turned out to 21 centres around the country on Saturday to protest the proposed deal, anti-TPPA group It's Our Future said.
They say the deal could end up hurting National at the polls.
Mr Key said protesters should wait to see the deal.
"Fundamentally on the things I've seen it's progressing pretty well," he told the Paul Henry programme on Monday.
"There's bits of dairy that we need to be resolve and we're hopefully making progress there, but overall it's good for the country."
He suggested those against it should look at any free trade deal New Zealand had signed and "show me one we want to rip up".
Mr Key said all free trade deals were designed in secret.
Some protesters would never accept a free trade deal, while others were protesting under a bit of misinformation, he said.
"They worry about drugs and things, but all the things I've seen are very, very manageable."
Mr Key was confident once those people saw they deal, they would be able to accept it.
"There's three groups – some are Jane Kelsey and her people; she's been opposed to every single free trade deal… she'll never agree. The second group are the Labour and the Greens people; they are there with all sorts of stuff… Labour in their heart of hearts are actually in favour, but they're in that oppositional mode at the moment where they're opposed to everything… then you get to the third bit with people who are genuinely protesting, but I think protesting on quite a bit of misinformation."
The most recent round of TPPA talks in Hawaii failed to net a final agreement, but trade ministers from the 12 countries have said they're still confident a deal can be reached.
NZN / 3 News