A landmark deal covering a significant proportion of the world's trade has inched closer to reality, despite ongoing divisions between Japan and the United States at talks in Sydney.

Now into its fourth year of negotiations, the Trans Pacific Partnership (TPP) will cover almost 40 per cent of the world's economies and set boundaries for global commerce between 12 countries, including Australia.

"I have felt that the entire focus has gone up several notches," Trade Minister Andrew Robb said following three days of meetings in Sydney.

"There is a real sense we are within reach of the finish line and the prize looks very attractive.

"But with these types of agreements, nothing is decided until everything is decided."

The TPP will cover countries with a combined GDP of about US$27,750 billion.

But one issue that needs sorting out is market access between the US and Japan.

Akira Amari, Japan's state minister in charge of TPP talks, said there was still a gap between the countries over access to Japan's protectionist agriculture sector.

"Today I had a bi-lateral meeting (with the US) and we have seen considerable progress," Mr Amari said.

"But still, some important issues are remaining and at this point in time we cannot say that there is a clear prospect of a US/Japan market access negotiation to be concluded."

Over the past three days the delegates scrutinised major TPP issues, including intellectual property and the influence of state-owned enterprises.

When pressed on how the TPP will affect future medical test data, Mr Robb said the negotiations couldn't be made public.

"We need to make sure the package has been decided before we release a whole lot of the detail," he said.

Dr Patricia Ranald of the Australian Fair Trade and Investment Network told SBS she wanted a draft text of the TPP agreement.

"My academic discipline is international trade,” she said. “I am not anti-trade but I don't want trade agreements which extend monopoly rights at the expense of people’s rights.

"With free-trade agreements the devil is in the technical detail; if you can't see the text you don't really know what's there."

The plan has been criticised for its secrecy, amid fears it will increase the cost of pharmaceuticals and have implications for domestic intellectual property rights.

Doctors Without Borders and WikiLeaks have criticised the TPP, saying it will threaten cheap access to medicines, while other groups have criticised the intellectual property arrangements, which they say will damage national sovereignty.

US trade ambassador Michael Froman said the TPP would not undermine any nation's authority.

"The work we are doing is to ensure our governments can regulate in the public interest, while we provide the kind of investment protections that are necessary to ensure strong flows of trade and investment around the world," Mr Froman said.

Separate negotiations by representatives from the 12 countries are continuing this week.