TAIPEI/MANILA -- The chances of an armed clash in the South China Sea appear to be rising fast, even as China paints a picture of regional harmony while it works with Southeast Asian neighbors on a code of conduct for the crucial waterway.

Chinese Foreign Minister Wang Yi told reporters in Beijing on March 8 that China and others in the region seek to conclude talks on the code by 2021. Wang said this will provide "stronger safeguards for safety and freedom of navigation in the South China Sea and enable China and ASEAN to build trust, manage disagreements, strengthen cooperation and maintain stability."

Yet Wang did not address the intensifying friction between China and two of its maritime neighbors, Vietnam and the Philippines. Given China's militarization of the reefs and islands it already holds in the Paracel and Spratly chains and its push to assert control over geographic features administered by others, a conflict in the sea -- potentially involving the U.S. -- seems to be becoming more of a question of when, rather than if.

In a sign of growing concern in the Philippines, the government has begun to openly question its decades-old Mutual Defense Treaty with Washington. The Spratly Islands to the country's west have seen a recent buildup of Chinese vessels.

"The Philippines is not in a conflict with anyone and will not be at war with anyone in the future," Philippine Defense Secretary Delfin Lorenzana said in early March. "But the United States, with the increased and frequent passage of its naval vessels in the West Philippine Sea, is more likely to be involved in a shooting war. In such a case and on the basis of the MDT, the Philippines will be automatically involved." The West Philippine Sea is the Philippines' term for the South China Sea.

Tensions are also rising to the west, around the Paracel Islands. Two days before Wang's comments, a Chinese vessel rammed and sank a Vietnamese fishing boat near Discovery Reef in the Paracels, according to Hanoi. The Paracels are home to overlapping claims by Vietnam, China and Taiwan. The five fishermen on the Vietnamese boat were eventually rescued, Hanoi said.

In early March, Philippine media reported that China had effectively asserted control over sandbars near the Philippine-administered Thitu Island, in the Spratlys. The sandbars, which are adjacent to bountiful fish stocks, had previously been frequented by Philippine fishing boats, which are now being turned away by what are effectively Chinese paramilitary boats posing as fishing vessels.

Worries in the Philippines over the fate of Thitu are growing. The mayor of the town of Kalayaan, which is responsible for Thitu told local media he personally witnessed a Chinese helicopter fly over the island before returning to Subi Reef in late January. In 2012, China dislodged the Philippines from Subi Reef, just 24 km away, subsequently militarizing it and building a runway there.

Filipino defense officials "are naturally wary of the Chinese fishing vessels around Pag-asa Island," said Jay Batongbacal, director of the Institute for Maritime Affairs and Law of the Sea in Manila. "The possibility that China might seize control of the island through unarmed militiamen has been on their minds."

Batongbacal added that "China's recent activities near Pag-asa is part of its so-called 'cabbage strategy' of saturating contested maritime features and spaces with ostensibly nonmilitary assets and activities that constrain another claimant's freedom of movement."

The fishing vessel militia is backed up by two additional layers: the China Coast Guard and the PLA Navy.

That cabbage strategy was perfected by China in waters also claimed by Vietnam in 2014, when it deployed the Hayang Shiyou 981 deepwater drilling rig, said Greg Poling, director of the Asia Maritime Transparency Initiative.

A Chinese oil rig in waters also claimed by Vietnam © Reuters

"There are hundreds of Chinese fishing vessels present at Subi and Mischief reefs on any given day and they aren't fishing, as is clear from satellite imagery," along with radar and other tools, he said. "Their primary purpose is to serve as the front line in China's assertion of sovereignty over the Spratlys, and that primarily means intimidating the neighbors when they do things China doesn't like."

The boats, Poling said, serve as "eyes and ears" for the Chinese Navy and Coast Guard."

The American role in the South China Sea is a major variable. While in Manila on March 1, U.S. Secretary of State Mike Pompeo made the strongest statement of support to date for the Philippines in its territorial dispute with China.

"Any armed attack on Philippine forces, aircraft or public vessels in the South China Sea would trigger mutual defense obligations under Article 4 of our Mutual Defense Treaty," Pompeo told reporters.

Speaking in the U.S. on Tuesday, Pompeo accused China of blocking Southeast Asian countries from developing energy resources in the sea through "coercive means." This prompted Chinese Foreign Ministry spokesman Lu Kang to fire back on Wednesday: "Nations outside the region should refrain from stirring up trouble and disrupting the harmonious situation."

Meanwhile, a U.S. Navy flagship was anchored in Manila Bay on Wednesday. Captain Eric Anduze, commander of the USS Blue Ridge, reiterated a vow to "sail, fly and operate wherever the law allows us to."

With the South China Sea part of a global power struggle between Beijing and Washington, China has opposed the U.S. Navy's freedom of navigation operations in the contested waters. China also rejects diplomatic criticism from the U.S. regarding the sea.

"We welcome well-intentioned advice, but do not accept deliberate smears or interference," Wang, China's foreign minister, said in his March 8 news conference, making a veiled reference to the U.S. "The countries in the region should grasp in our own hands the key to peace and stability in the South China Sea."

At the same time, however, both Beijing and Southeast Asian capitals seem to be questioning the credibility of commitments by the Trump administration to keeping the increasingly militarized waters of the South China Sea open under its Indo-Pacific strategy.

"I think the concerns people had when [Trump] got elected have only become aggravated and his foreign policy after more than two years only confirms the worry that he is not committed to Asia," said Huong Le Thu, senior analyst at the Australian Strategic Policy Institute.

In an interview with the Nikkei Asian Review, Philippine Navy Chief Robert Empedrad backed Washington's freedom of navigation operations despite Beijing's allegations that such moves are raising tensions.

"The West Philippine Sea is an open sea," Empredad said.

China has maritime territorial disputes with four of ASEAN's 10 members -- the Philippines, Vietnam, Malaysia and Brunei -- and growing tensions with Indonesia near the south end of the sea. But pushback from the bloc, where China's massive influence over Cambodia and Laos has prevented even mild statements regarding the South China Sea, is unlikely.

While Beijing's divide-and-conquer tactics may work in ASEAN, it is far from clear if the pressure it is putting on the U.S. will be as successful.

The result? The perfect conditions for miscalculation, perhaps triggered by overzealous Chinese "fishermen."

"Sooner or later there will be a violent incident, most likely involving those militia and a Filipino or Vietnamese vessel, which will escalate to involve naval forces before anyone can stop it," Poling warned. "And if the Philippines is involved, there is a good chance the U.S. will be dragged in without China actually intending for that to happen."