Asean has to get used to new internal dynamics as each member - to a different degree - feels the influence of burgeoning regional powers, especially China and India, said Prime Minister Lee Hsien Loong.
But this must not lead to a divided Asean, he said yesterday.
"We must accept the reality of these tidal pulls, without allowing them to lead to fault lines forming within the Asean group," he said.
New powers, especially China and India, are growing in strength and influence, creating new opportunities, he noted. At the same time, "countries have to take into account the policies and interests of new powers, while maintaining their traditional political and economic ties".
In the United States, the political mood has changed. But Asean hopes the world's biggest economy and region's security anchor remains active in South-east Asia.
"In this shifting environment, it is important that Asean works actively to maintain its centrality and relevance," the Prime Minister told about 500 people, including diplomats and students, at a lecture marking the 50th anniversary of think-tank ISEAS - Yusof Ishak Institute.
He noted that there is nothing to prevent other groupings or projects - such as China's Belt and Road Initiative - from being launched. "Amid this Darwinian process, Asean members must come together to maintain Asean's relevance and cohesion."
Thus, while each Asean member has its own domestic issues to manage, a unified front is key. PM Lee called on governments to invest political capital in the Asean project and to make a conscious effort to think regionally, not just nationally.
For example, the Regional Comprehensive Economic Partnership, which comprises Asean and its six free trade agreement partners, and the Asean-European Union Comprehensive Air Transport Agreement will involve significant trade-offs and compromises, he said.
"But I hope governments will take a long-term approach, assess their enlightened self-interests, and make bold decisions which will improve our people's lives," he said, adding that this is what has brought Asean to where it is today.
Tackling an often-cited criticism of the Asean decision-making process - which is built on consensus, PM Lee acknowledged it can be slow and unwieldy.
But it has its merits, he said.
"Asean, once it has arrived at a decision, does not change its position lightly. External partners therefore see value in deepening their engagement of the region through Asean."
Singapore, which is chairing Asean this year, will initiate projects to strengthen the group's resilience against threats such as terrorism, cybercrime and climate change, said PM Lee. At the same time, it will help Asean economies to innovate and use technology.
In a dialogue that followed, PM Lee was posed questions ranging from Asean relations with the major world powers to the impact of the Belt and Road Initiative. It was moderated by Ambassador-at-Large Tommy Koh.
Professor Dewi Fortuna Anwar of the S. Rajaratnam School of International Studies asked how Asean can maintain its unity as various members desire to advance their relations with a growing China.
PM Lee said there is a gradient among its countries in terms of their attitudes towards powerful nations like China, and they may differ in "where they line up" when issues such as the South China Sea dispute arise. But it is better to deal with these within the grouping, where the 10 members can strive to reach consensus, even though it may be a longer process than if the group had been smaller.