China and Southeast Asian countries struggled to make progress on a code of conduct designed to ease tensions in the disputed South China Sea, diplomatic sources have said.

The two sides were due to meet ahead of a summit of the 10-member Association of Southeast Asian Nations (ASEAN) in Cambodia amid splits on what the code should include and how it should be implemented.

While the issue is not on the formal agenda for the ASEAN summit beginning on Thursday, it was raised informally by members and discussed during a separate ASEAN-China dialogue on Wednesday.

A joint statement to be issued by ASEAN foreign ministers was also held up as countries wrangled over whether to include a reference to recent spats over the resource-rich area pitting China against Vietnam and the Philippines.

"ASEAN foreign ministers are having an emergency meeting to resolve the wording on the South China Sea in the joint statement," one Asian diplomat told AFP news agency on condition of anonymity on Wednesday.

Pact expected

Another spoke of "splits and divisions" in the organisation, principally between the Philippines and the chair of the meeting, staunch Chinese ally Cambodia.

Marty Natalegawa, the Indonesian foreign minister, admitted the debate about whether to mention recent incidents, including a standoff between Philippine and Chinese ships last month over Scarborough Shoal, remained a sticking point.

The shoal, an outcrop in the South China Sea, is claimed by both countries.

"It's very important for us to express our concern with what happened whether it be at the shoals, whether it be at the continental shelves," he told reporters.

"But more importantly than simply responding to the past is to move forward to ensure that these kind of events no longer occur."

ASEAN, currently chaired by Cambodia, had aimed for a code to be hammered out this year.

China rejects any international intervention in settling the overlapping territorial claims and wants to discuss the differences bilaterally with concerned countries.

Clinton arrival

Manila is leading a push for ASEAN to unite to persuade China to accept a code of conduct based on a UN law on maritime boundaries that would delineate the areas belonging to each country.

US Secretary of State Hillary Clinton is to arrive in Cambodia for a wider regional Asian summit on Thursday, with Washington also pushing for progress on reducing friction in a key shipping lane that is vital to the world economy.

"We look to ASEAN to make rapid progress with China toward an effective code of conduct in order to ensure that as challenges arise, they are managed and resolved peacefully," Clinton said in Vietnam on Tuesday.

She said that the South China Sea would be discussed alongside other areas of mutual concern at the ASEAN Regional Forum, which groups 26 Asia-Pacific countries and the European Union and starts on Thursday.

This risks irking Beijing after the Chinese foreign ministry warned on Tuesday against "hyping" the problem and said it should be kept out of the summit.

"This South China Sea issue is not an issue between China and ASEAN, but between China and some ASEAN countries," Liu Weimin, China's foreign ministry spokesman, told reporters.

"Hyping the South China Sea issue... is against the common aspirations of the people and the main trends of the time to seek development and cooperation."