UPDATED 3.42pm: The Prime Minister admits New Zealand may have to pay more for pharmaceuticals, for a period, under the Trans Pacific Partnership Agreement.

John Key made the admission as officials sit down in Hawaii for a make or break session on the free trade agreement

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Mr Key said the drugs will be more expensive.

"The government will have to pay for the original drug as opposed to the generic for a little bit longer, but for consumers that won't make any difference because on subsidised drugs you pay $5 for your prescritions."

John Key said if necessary the Government will increase the budget of its drugs buying agency Pharmac.

And he says because we'll be earning more tax under the TPP, even more drugs could be funded.

"We always look at these things on the balance of benefits. On the advice I've had so far, remembering the deal hasn't been completed yet, New Zealand gains more than it loses."

However Labour leader Andrew Little is voicing his concerns over the PM's comments.

He said they want Pharmac's purchasing model protected.

"If that bottom line isn't met, then we won't support the TPP."

"This is at odds with what the government has been saying. Now we see that Pharmac is likely to cost the taxpayer a lot more."

The Prime Minister has earlier been on the attack over the Labour party's views on the TPP free trade deal.

Andrew Little said his party won't back the trade deal if it undermines the country's sovereignty.

He said Labour is not opposed to free trade, but the agreement must be in the best interests of New Zealanders and that includes the right to ban foreign buyers of property here.

"If it compromises or prevents the ability of a future government to restrict land sales, residential or farm or bans or whatever form it might take, we will be opposed to the TPP."

But John Key's calling Labour's stance crazy and schizophrenic.

"Are you really telling me Phil Goff - who seems to have dedicated his career to trade and opening up trade, along with Clayton Cosgrove and a lot of others - really believe it's in New Zealand's interest not to sign a Free Trade Deal with the biggest economy in the world, and the 4th biggest economy in the world? It's just barking madness."

New Zealand First and the Greens also oppose the deal.

Auckland University Professor Jane Kelsey's urging people to get on the phone to the offices of John Key and Tim Groser in the next four days in the hope of getting them to walk away from the TPP deal.

Jane Kesley is calling on John Key to release the whole of the text of this agreement so we can see what other surprises are there.

"The things that are really mattering to us are still on the table and people need to send a clear message to the Prime Minister now that we don't want this deal."

John Key believes he can secure the votes in the House to pass any law a TPP agreement would need, and has indicated he expects the support of United Future MP Peter Dunne.

The TPP trade deal involves 12 nations, including the Australia, the United States and Japan.