Reports of an agreement between the United States and Australia over protections for biologic drugs have raised hopes of a final deal on a Pacific trade pact.
Japanese and other media reported on Sunday that US Trade Minister Michael Froman and Australia's Trade Minister Andrew Robb overcame differences that were the main roadblock to a final agreement.
The authoritative Inside US Trade website said the two had circulated to other ministers a compromise proposal on how many years of protection are to be accorded creators of the cutting-edge class of drugs sourced from living materials.
A US official at the talks confirmed that "there is progress" on the issue, but would give no details.
Biologics are proving valuable sources of treatments for everything from arthritis to cancer.
A ministerial meeting broke up after only about 15 minutes near midnight on Saturday with others blaming the two countries for holding up a final deal for the Trans-Pacific Partnership, a free-trade pact that would comprise around 40 per cent of the global economy.
Froman met with Robb first thing on Sunday morning, which officials said would be the last day of negotiations after having extended them from the expected close on Thursday.
After failing to reach a final deal on the Pacific Trade Partnership in Hawaii in July, the ministers are under heavy pressure to do so now.
Japan's Economy Minister Akira Amari has made clear he will not stay another day, as he is due back in Tokyo for a cabinet reshuffle.
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.