ATLANTA (AFP) - Officials negotiating an ambitious Pacific trade pact could announce a deal "in principle" on Sunday (Oct 4) after days of gruelling talks, Japan's Economy Minister Akira Amari said.

Mr Amari told Japanese journalists that there had been "major progress" on Sunday morning and that a solution had been found to the main roadblock to a deal, how to protect developers of biologic drugs. The United States and Australia had been sharply divided on the issue.

"We are making preparations now to announce a deal in principle this afternoon," he said, according to a translation of his remarks supplied by Japanese journalists.

That suggested there would still be some loose ends to wrap up after five days of ministerial talks in Atlanta on what will be the world's largest free trade zone, the Trans-Pacific Partnership (TPP).

The talks between representatives of 12 countries comprising 40 per cent of the global economy - including Canada, New Zealand, Mexico and others - have gone three days past the scheduled ending and Mr Amari made clear he was not willing to extend another day.

The administration of President Barack Obama, the prime driver behind the TPP, wants it to create a foundation for "21st century trade rules", setting standards on trade, investment, data flows and intellectual property that eventually non-TPP members - particularly China - will have to accept.