LAHAINA, Hawaii (REUTERS) - Talks on a Pacific Rim free-trade pact faced a fast-approaching deadline on Friday as trading partners aimed to wrap up a deal within hours, with issues including trade in dairy products and monopoly periods for next-generation drugs still unresolved.

Trade ministers from the 12 nations negotiating the Trans-Pacific Partnership, which would stretch from Japan to Chile and cover 40 per cent of the world economy, had a news conference scheduled for 1.30pm local time (7.30am Singapore time) on the Hawaiian island of Maui.

"We are still aiming to conclude the negotiations by the time of the news conference," Japanese Economy Minister Akira Amari said before heading into a plenary session.

"Some countries are insisting on enormous demands and that's the cause of the impasse."

Dairy exports are a top sticking point, with New Zealand - which has said it will not back a deal that is not good for dairy - and Australia seeking more access to Japanese, Canadian and US markets.

John Wilson, chairman of the world's largest dairy exporter, New Zealand dairy cooperative Fonterra, arrived to attend the talks late on Thursday to press home the case.

"It's still dire. This thing is now on a knife edge. There is still not enough in this for New Zealand at all," said Mike Petersen, who represents New Zealand's farm sector.

Ministers have also yet to agree on how long to protect data used to develop biologic drugs.

US drugmakers want 12 years, but Australia wants five.

People briefed on the talks say a compromise on seven or eight years seems likely, but Mexican Trade Minister Ildefonso Guajardo stressed no deal was done.

"That is exactly what we are trying to negotiate," he told reporters on his way into the meeting.