Thailand's export market share in Asean is likely to decline once the Asean Economic Community takes shape, with Singapore and Malaysia busy revving up their manufacturing presence in Cambodia, Laos, Myanmar and Vietnam.
According to Aat Pisanwanich, director of the Center for International Trade Studies at the University of the Thai Chamber of Commerce (UTCC), Thai shipments to the four emerging neighbours will take a hit over the next five years.
Stiff competition will come not only from strong Asean members but also China.
Mr Aat suggested the government speed up marketing plans for emerging Asean countries to protect Thailand's market share.
A UTCC study found that Thailand raised shipments to Asean over the last five years, with the bloc now taking in 25% of Thailand's exports, up from 22.7% in 2010.
Malaysia, Singapore and Indonesia are the big markets, accounting for more than 50% of Thailand's Asean shipments.
The UTCC divides Asean into old and emerging markets. The old markets are Singapore, Indonesia, Malaysia, the Philippines and Brunei, and the emerging markets are Cambodia, Laos, Myanmar and Vietnam.
In 2014, old markets were valued collectively at 8.9 trillion baht, with emerging markets worth 1.5 trillion baht.
Thailand's market share ranked third in old markets (13.8%), trailing Malaysia (21.3%) and Singapore (39.5%).
In emerging markets, Thailand was No.1 (44.1%), followed by Singapore (35.7%), Malaysia (11.8%) and Indonesia (7.4%).