US President Barack Obama was on Tuesday set to defy Beijing's protests and use a summit to raise concerns over South China Sea rows that have sent diplomatic and trade shockwaves across the region.

Obama planned to pressure China on the highly sensitive issue of a code of conduct that would govern behaviour in the contested waters, according to a senior aide to the president, Ben Rhodes.

"We... want to see continued momentum on the diplomatic process. ASEAN needs to talk to China about a code of conduct," Rhodes said, referring to the 10-member Association of Southeast Asian Nations.

Obama was set to hold talks on Tuesday afternoon with Chinese Premier Wen Jiabao and the leaders of ASEAN nations and other countries in the region, on the final day of the annual East Asia Summit.

He had earlier in the day held one-on-one talks with Wen.

Obama is on the final leg of a three-nation trip to Asia aimed at deepening Washington's influence in the region and countering the rise of China.

Repeating a long-held Chinese position, Wen insisted on Monday that the maritime disputes should not be "internationalised" and discussed at multilateral events such as the summit.

China, which claims sovereignty over virtually all the South China Sea, prefers to negotiate directly with its neighbours from the 10-member Association of Southeast Asian Nations (ASEAN).

ASEAN members Vietnam, the Philippines, Malaysia and Brunei, as well as Taiwan, also have claims to parts of the sea, which is home to some of the world's most important shipping lanes and believed to be rich in fossil fuels.

The rival claims have for decades made the sea a powder keg issue in the region. Chinese and Vietnamese forces engaged in clashes in 1974 and 1988 in which dozens of troops died.

After a long period of relative calm, tensions have risen over the past two years with the Philippines and Vietnam expressing concerns that China is becoming increasingly aggressive in staking its claim.

Some bruising diplomatic confrontations this year have overshadowed regional meetings where the participants typically prefer to focus on improving economic ties.

At the East Asia Summit, the first day was dominated by infighting over the issue among the ASEAN bloc.

Cambodia, this year's ASEAN chair and a close Chinese ally, said the 10 nations had agreed not to "internationalise" the disputes, which would have given China an important diplomatic victory.

But the Philippines quickly denied that it had agreed, with President Benigno Aquino rebuking Cambodian Prime Minister Hun Sen during one of the meetings on Monday.

"How can there be a consensus? A consensus means 100 percent. How can there be a consensus when two of us are saying we're not with it," Philippine Foreign Secretary Albert del Rosario told reporters afterwards.

He said later the other country that did not agree was Vietnam.

The feud echoed unprecedented infighting at an ASEAN foreign ministers' meeting in Phnom Penh in July, which ended for the first time in the bloc's 45-year history without a joint communique.

The Philippines and Vietnam had wanted the statement to make specific reference to their disputes with China, but Cambodia blocked the moves.

Despite the tensions, leaders are expected to make progress on important economic issues on Tuesday.

ASEAN nations are set to officially launch negotiations to create an enormous free trade pact with China, Japan, India, South Korea, Australia and New Zealand.

Trade ministers from China, Japan and South Korea are set to hold talks aimed at kick-starting three-way free trade negotiations.