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

The two sides were due to meet at 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.

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 on condition of anonymity.

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

Indonesian Foreign Minister Marty Natalegawa 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."

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.

Beijing has said it is prepared to discuss a more limited code aimed at "building trust and deepening cooperation" but not one that settles the territorial disputes, which it wants to negotiate with each country separately.

ASEAN Secretary General Surin Pitsuwan told reporters Wednesday that the fact the code was under discussion "is already having a calming effect on all parties".

Efforts to produce one began 10 years ago, but nations were now engaging seriously and efforts were being made to "move along", he said.

Planned talks between ASEAN and Chinese Foreign Minister Yang Liechi were repeatedly delayed, however, with a meeting originally scheduled for the morning slipping to a late afternoon slot.

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 (ARF), which groups 26 Asia-Pacific countries and the European Union and starts 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," foreign ministry spokesman Liu Weimin 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."