The leaders of the 10 ASEAN member nations - Myanmar, Brunei, Cambodia, Philippines, Indonesia, Laos, Malaysia, Singapore, Thailand and Vietnam - will hold a plenary session in the afternoon to officially start the summit, reports Efe news.
Security, trade, investment and measures to combat pollution were among the issues that will be addressed at the annual meeting of the regional bloc, whose rotating chair is held by Thailand this year.
Thai Prime Minister Prayuth Chan-ocha had extended a formal invitation in Washington last month to US President Donald Trump, who had initially agreed to attend the summit.
But, Trump subsequently decided to send a delegation, led by Commerce Secretary Wilbur Ross and National Security Adviser Robert O'Brien, who will take part in the ASEAN-US summit as well as the East Asia Forum, both scheduled to be held on November 4.
The scaled-back US delegation contrasts with that from China, which, with Prime Minister Li Keqiang at its helm, will seek to expand its influence in the region.
China, which has been locked in a trade dispute with the US for the past one-and-a-half years, is the main driving force behind an ambitious multilateral trade pact that was launched during the 2012 ASEAN summit in Cambodia.
The agreement, if finalized, will cover a population of 3.4 billion people - 47 per cent of the world population - and involves a GDP worth $22.6 trillion (32.2 per cent of the world).
The agreement also brings together 29 per cent of the current world trade and 32.5 per cent of global investment.
The negotiations for the Regional Comprehensive Economic Partnership (RCEP), as this pact between 16 countries from the Asia and Oceania region is called, could conclude in the summit in Bangkok.
The RCEP, which, besides China, also includes India, Australia, China, South Korea, Japan, New Zealand and the 10 ASEAN members, emerged as Beijing's answer to the Trans-Pacific Partnership (TPP) agreement that Washington had been pushing for over the last decade before Trump took office.
ASEAN, founded in 1967, accounts for a population of 647 million which aims to raise its combined GDP to $4.7 trillion by 2025 and become the world's fourth-largest economic power.
( With inputs from IANS )