Prime Minister John Key is urging the United States not to lose sight of the benefits of the Trans-Pacific Partnership Agreement.

John Key has given a speech to the Council on Foreign Relations in New York today, ahead of his General Assembly address at the United Nations tomorrow.

He said the United States would suffer a "massive lost opportunity" if it does not pass the TPP in November or December. 

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Mr Key said it was be a loss not only for US consumers and businesses but would also be a loss for the potential expansion of the deal to countries such as China, Indonesia and South Korea.

Presidential nominees Donald Trump and Hillary Clinton say they would renegotiate the deal among 12 countries.

President Barack Obama's so-called lame-duck period, after the presidential elections but before the winner in sworn in in January, is his last opportunity to get the deal through under his Administration.

Mr Obama's position is that the US must ratify it or China will set the global trade agenda.

"If TPP fails to get ratified during the lame-duck period, it will be a massive lost opportunity for the United States both for their consumers and business but also for the geopolitics of the region," Key told about 80 members of the Council for Foreign Relations in New York.

"Because in the end if that vacuum isn't filled by the United States, it will be filled by somebody else."

"We think the United States is in a really pivotal point because if it is not passed in the lame-duck period, the question is will it ever be passed?

"When people say the deal can be modified and the parties can come back to the table, that relies on those 12 countries having the will to do that."

"There's a deal there. The deal is ready to be signed and in our view it is massively in the United States' interests to sign that deal."

The 12-nation agreement, covering 40 per cent of global trade and 800 million people, was signed off in October last year.

To take effect it must be ratified by at least six countries that account for 85 per cent of the group's economic output, which makes the US essential.

The partner countries are New Zealand, Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, Peru, Singapore, the United States and Vietnam.

Additional reporting by Audrey Young of the New Zealand Herald and NZ Newswire