India, Sept. 11 -- A spat between the world's most populous countries is holding up a pan-Asian trade agreement encompassing nearly a third of all global trade.

Trade ministers from 16 Asia-Pacific countries this week hailed a "critical milestone" after seven years of talks and vowed to wind them up before a regional summit in November. But officials involved in the process say major sticking points remain around market access and the ability of workers to find employment in other countries.

The main source of tension is between India and China over the amount of goods with preferential tariffs, according to a person familiar with the negotiations who asked not to be identified. The person said India was also unhappy with the position o...