Fifteen Asia-Pacific economies are set to conclude talks on Sunday and sign what could become the world's largest free trade agreement, covering nearly a third of the global population and about 30 percent of its global gross domestic product.

The Regional Comprehensive Economic Partnership (RCEP), which could be approved at the end of a four-day Asan Summit in Hanoi, will progressively lower tariffs and aims to counter protectionism, boost investment and allow freer movement of goods within the region...