China's latest actions off Vietnam this past week have been seen as highly provocative and have triggered clashes with Vietnamese coast guard vessels.
Asean government leaders meeting in Myanmar's capital this weekend are also expected to respond sternly to China's actions.
Myanmar, as the summit host, will play a crucial role in determining the tone of the final Asean statement on China, its northern neighbour and main foreign investor.
The region's foreign ministers, however, insist it is time to take a stand.
"In the spirit of centrality and unity, Asean will come up with a common position to uphold the peace and security in the region," Philippine Foreign Secretary Albert del Rosario told Kyodo News.
Singapore Foreign Minister K. Shanmugam said Asean "can't stay silent" this time.
"We have to be neutral. Vietnam will have one version, China will have another version of the events," he said. "It's difficult for Asean to take sides but neutrality doesn't mean staying silent."
Speaking to reporters after the meeting, Shanmugam said, "Our credibility has been affected a little in the last few years.
"If these events took place a few days ago and Asean foreign ministers meet here today, leaders meet tomorrow and we didn't say anything, I think our desire to play a central role, our desire to be united, our desire to have a peaceful region, all of this, and Asean's own integrity, I think, will be seriously damaged."
He was referring to the failure of Asean leaders to jointly condemn similar Chinese actions two years ago. At the time, Cambodia was chairing the group and Prime Minister Hun Sen was accused of actively blocking efforts to take a stand for fear of losing Chinese investment.
Vietnam, which denounced Chinese ships' ramming and firing water cannons at its vessels, raised the issue at the meeting of senior Asean officials Friday.
An Asean diplomat told Kyodo News that the Philippines supported Vietnam, saying China's recent actions violated international law and the Declaration on the Conduct of the South China Sea, which Asean and China signed in 2002.
The Philippines also briefed Asean on the progress of its case against Chinese incursions into its territory at a UN tribunal, according to the diplomat.
The diplomat said Indonesian Foreign Minister Marty Natalegawa expressed concern at the slow consultation process to craft a legally binding code of conduct in the South China Sea.
Asean is concerned that the standoff in the waters claimed by both China and Vietnam might deteriorate into an armed conflict that could hurt regional stability and delay plans to transform Southeast Asia into a community by 2015.
Sihasak Phuangketkeow, permanent secretary of Thailand's Foreign Ministry, said Asean was very concerned about the situation and was seeking a "constructive" statement that "reflects our common concern".