Trade ministers from 12 Asia Pacific countries made more progress on an ambitious regional pact here, but the end is still not in sight.

The latest round of talks ended on Tuesday with no clear signs of a time-frame as to when the deal will be concluded.

"We made further strides toward a final agreement," it was noted in a joint statement from the 12 ministers.

"We have agreed on the majority of the landing zones identified at our last meeting. While some issues remain, we have charted a path forward to resolve them in the context of a comprehensive and balanced outcome."

The central issue of market access is among several key outstanding ones yet to be resolved.

"Market access is in some respects the heart and soul of any trade agreement so until that's done, we don't have an agreement," New Zealand Trade Minister Tim Groser told a press conference after the talks.

The TPP nations are Australia, Brunei, Chile, Canada, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam. They account for nearly 40 per cent of global economic output and about one-third of all world trade.

More significantly, the nations are a massive market for Singapore businesses, with 790 million people and total economic output of about US$28 trillion (S$35.5 trillion) in 2012. They made up nearly $300 billion, or more than 30 per cent, of Singapore's goods trade in 2012, and include several key trading partners.

The TPP also "serves as a possible pathway" to an Asia-Pacific free trade area, Singapore's Ministry of Trade and Industry noted in a recent statement.