At the summit, the diplomatic squabbles kicked off with Japanese Prime Minister Shinzo Abe's keynote speech on May 30. He said Japan should play a greater role as a protector in the region.

Abe said Tokyo would support Southeast Asian countries with, for instance, patrol vessels, as they sought to protect their borders against incursions by Beijing. "Japan will offer its utmost support for the efforts of the countries of Asean [Association of Southeast Asian Nations] as they work to ensure the security of the seas and the skies," Abe said.

The next day, US Defence Secretary Chuck Hagel was more blunt. He accused Beijing of de-stabilising the region through intimidation and coercion.

"The United States will not look the other way when fundamental principles of the international order are being challenged," he said.

Wang Guanzhong , deputy chief of the general staff of the People's Liberation Army and head of the Chinese delegation to the meeting, said Hagel's speech was "full of hegemony" and could cause instability.

Wang said the attacks on China by the US and Japan appeared to be "coordinated". "Abe and Hagel's speeches gave me a feeling that they were singing a duet," Wang said. "They supported and encouraged each other and used their speeches to instigate provocations against China."

As the great powers traded barbs, the region's security and strategy leaders watched with concern.

Some delegates applauded Abe's ambition , but others said they worried that the competition for influence could exacerbate tensions.

Carl Thayer, of the University of New South Wales at the Australian Defence Force Academy, said the smaller nations were like corks floating "in the ocean with big powers smashing the water". "How do they stay in the centre and not get pushed aside?"

Participants who would welcome a greater security role for Japan said it would be a counterbalance to China's increasingly assertive behaviour in the South China Sea. It was particularly well received among delegates from Vietnam and the Philippines, which have territorial disputes with China.

Others at the summit said that dealing with a democratic power like Japan would afford greater predictability, something China did not offer.

Indonesian delegate Dewi Fortuna Anwar said that in the 2000s, China was a neighbour that would "go out of its way" to foster friendly relationships with Asean countries.

But since about 2008, Beijing had become more aggressive and started to "push itself forward", leaving the region puzzled, the academic said.

"It's easy to build distrust, but to restore trust takes a long time. And we like predictability," said Anwar, who is a senior adviser to Indonesia's vice-president. "You cannot put your charm on and off. There has to be some predictability."

China, which still bitterly remembers Japan's wartime atrocities, has warned that Abe's plan to change the country's defence policy would signal a return to militarism.

But Anwar said Japan had enough checks and balances to prevent that from happening.

Before he goes much further, Abe must convince a wary public at home of the benefits of dispatching troops to play regional protector.

Japan's constitution forbids the Self Defence Force from doing anything beyond protecting its own territory. Abe and his Liberal Democratic Party are now seeking to reinterpret the "no war" provisions so that the defence forces can participate in so-called collective self-defence - aiding allies that are under attack and protecting its citizens abroad.

Abe's speech at the Shangri-La Dialogue concerned some delegates.

"The region is divided. Not everybody here outright opposes Japan," Thayer said. "But some are quite worried that the major powers could overplay their hands."

For years, Beijing has seen Washington's strategy to reengage with Asia, termed a "pivot" in 2010 and later re-branded as "rebalancing", as a move to contain China's rise.

Relations between the two powers soured after US President Barack Obama's April trip to four Asian countries - three of them allies.

Many in China blamed Obama for further emboldening America's allies, in particular Japan and the Philippines, in their territorial disputes with China.

Nick Bisley, a professor of international relations at La Trobe University in Australia, said if events at the Shangri-La Dialogue were any indication, China was increasingly pitting itself against the US alliance.

That puts Southeast Asian nations in a tricky position.

"It's like 60 years ago when they were asked the 'which side are you on' cold war question," said Bisley, who attended the summit. "They sought to avoid that, and they are trying to avoid that. But it's not working."

In his speech, the PLA's Wang sought to advocate for a "new Asian security concept", a vision first outlined by President Xi Jinping a week earlier. Xi envisions a regional security framework in which China and other Asian countries would play a bigger role.

But barbs and heated exchanges overshadowed Wang's speech. Regional delegates also remained unconvinced when Wang said China never instigated problems but was forced to respond to provocations by others.

Similarly overlooked was a question raised by Singapore Defence Minister Ng Eng Hen in his concluding remarks: how best to accommodate a rising China?

Bisley and other analysts warned that a failure to find common ground would generate more friction. He said China was an insecure power, which could lead to rash decisions.

"The really tricky thing for the US to understand and to accept is that countries that depend on it, like the Philippines and Vietnam, have interests that ultimately matter less to the overarching system than China's," Bisley said.

"How it grapples with that is going to determine how things play out in the next 10 or 15 years."