Sixteen Asia-Pacific nations including Japan and China held their first round of talks Thursday toward forming one of the world's largest free-trade blocs.

At the five-day meeting on the Regional Comprehensive Economic Partnership through Monday in Brunei, the 10 members of the Association of Southeast Asian Nations and their six regional partners will discuss the scope and method for the talks. They want to reach a deal by 2015.

The RCEP would account for more than 3 billion people, or about half the global market and a third of global economic output, the Japanese government says.

In addition to a committee of senior officials, the 16 countries will set up working groups to focus on issues including trade in goods, trade in services, and investment, Japanese officials said.

The RCEP talks are taking place at the same time as other multilateral free-trade schemes, including the U.S.-led Trans-Pacific Partnership, which is about to make Japan its 12th member.

Prime Minister Shinzo Abe and senior government officials have said the TPP could become a foundation for the RCEP or an even greater free-trade agreement called the Free Trade Area of the Asia-Pacific.

But concluding the RCEP talks by 2015 won't be easy, given that the Asia-Pacific nations are looking for a deal that involves deeper engagement than ASEAN's existing free-trade agreements.

Japan, however, expects conditions for the RCEP to be less stringent than for the TPP, because the 16 nations would be allowed to retain certain tariffs.

ASEAN consists of Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam. Also involved in the RCEP talks are Japan, China, South Korea, Australia, New Zealand and India.

The 16 nations agreed in November last year to launch the RCEP negotiations after holding a series of meetings in 2011 that started with fewer members.