As leaders across Asia descend on Jakarta for the annual ASEAN and East Asia summits this week, one regional flashpoint is looming large.

For decades, five countries plus Taiwan have managed their competing claims in the South China Sea.

While sporadic skirmishes have occurred between boat crews in the contentious area, China's actions in the past few months are being seen by some as a marked escalation.

It may be the clearest sign yet that Xi Jinping's maritime forces believe they could seize the remaining Philippines-controlled islands if they choose to.

Recent incidents include the swarming of disputed reefs by Chinese fishing militia and coastguard boats as well as the use of a blinding laser on a Filipino coastguard boat.

Last month, Chinese crew were accused of deploying a water cannon on a Filipino supply boat, causing outrage in the country.

Several countries — including the United States and Australia — expressed concern over the incident, while the Philippines government summoned the Chinese ambassador to present a strongly-worded diplomatic protest.

China's actions have unsettled regional leaders still pinning their hopes on negotiations for a Code of Conduct for the disputed sea, despite 20-years of fruitless talks.

Some suspect China is stringing out the process, while consolidating its military bases and vessels in the area.

In the face of a David and Goliath battle to maintain control over the 11 islands and reefs still administered by Manila, the Philippines has turned to two very different forces: soldiers and holiday makers.

Fisherman and Chinese ships locked in tense stand off

Chinese coastguard vessels inside the Philippines' exclusive economic zone are nothing new to fisherman Lleser Caberoy.

The 47-year-old has been fishing in the South China Sea for two decades and says he's witnessed boats use water cannon to drive his crew away from disputed reefs.

He described an encounter near the disputed Second Thomas Shoal in April this year, which the ABC couldn't independently verify.

Zaldy Albi, a ferry captain who routinely delivers diesel to residents and troops of the main Philippines-controlled island, Pag-asa, says the Chinese fleets are ever present.

"If they see us approaching Ayungin Shoal on the way to Pag-asa, they will encircle our ferry with their coastguard ships and drive us away," he said.

The coastguard and fishing militia fleets are also present around Pag-asa, he said, but are more willing to let the Filipino crewed-ferry pass to deliver supplies there.

The Philippines coastguard and small naval boats provide some protection, the men say, but are outnumbered.

Ayungin, or the Second Thomas Shoal, appears to be China's priority for now.

The Philippines authorities, in a change of strategy, have started publicising videos of incidences at sea.

This includes the use of a water cannon in early August, which managed to stop one of two resupply boats reaching the Second Thomas Shoal.

Another resupply mission in late August managed to get through, but Beijing for the first time issued a statement claiming it "allowed" the resupply of food on "humanitarian grounds".

"China is setting up the stage where it can escalate in the future based on that rhetoric," said Justin Baquisal, a Manila-based analyst with FACTS Asia, a research organisation.

He believes the real flashpoint will come if the Philippines government pushes through with a plan to reinforce facilities on the decaying World War II-era ship.

A small group of Filipino troops rotate through the Sierra Madre, which the Philippines deliberately ran aground on the reef 24 years ago.

China's government defended the recent actions of its coastguard, claiming the resupply boats were trespassing on indisputable Chinese territory and were bringing building supplies to the ship.

Officials in Beijing say China's coastguard showed restraint and demanded the Philippines government tow the rusting ship away once and for all.

Australia and the Philippines engage in military drills

More than 1,000 Australian military personnel were involved late last month in the biggest bilateral series of exercises ever in the Philippines, including war games on the island of Luzon.

Their mission was clear: take back control of Philippines territory invaded by a mock enemy, involving a beach landing, parachute teams and simulated ground battles.

Other drills on another South China Sea-facing island, Palawan — along with exercises at sea — sought to bring Australian and Filipino forces closer than ever before.

"Australia and the Philippines have probably never been as strategically aligned as we are right now," declared Defence Minister Richard Marles, who travelled to the island of Luzon to observe the drills.

Sitting next to him was the country's President Ferdinand Bongbong Marcos Junior, who said he'll discuss deepening security ties further when Prime Minister Anthony Albanese visits Manila later this week.

Joint patrols that seek to enforce international law in disputed seas may even be announced when the two leaders meet.

"The Philippines cannot deter China on our own, so Manila is trying to normalise the presence of as many actors as it can, even if their militaries won't engage China," Mr Baquisal said.

"If the Philippines continuously holds military drills, China is going to think twice about any untoward moves in those areas."

The move towards joint patrols comes just months after Mr Marcos expanded base access to the US military, including one facility on Palawan near the disputed Spratley island chain.

After years of watching China build up military bases and wrest control of disputed reefs within the Philippines Exclusive Economic Zone, there's a fresh urgency in Manila.

And it's being cheered on by the people who see China's aggressiveness up close.

The Philippines is using a sneaky method to reassert its claim

Aside from military displays and coastguard patrols, the Philippines is sending in other boats in its quest to maintain control of the islands.

This year, small group tourism boats offering fishing and diving tours launched week-long voyages between Philippines-controlled islands, with plans to make the trips an annual fixture.

Ken Hupanda, a tourism officer in charge of the program, describes the trips as a "soft diplomacy" tool to reinforce Philippines claims.

"As long as we have the civilian and military personnel on the islands, I think there is no stopping us from using resources in the exclusive economic zone of the Philippines," he told the ABC in Puerto Princesa, where the voyages set off.

He says the Chinese ships monitor the tourism boats at close range, in what is an eye-opening scene for many patriotic Filipino tourists.

"I believe as long as they don't block the way, we will continue with the program," he said.

The long-term goal for the collection of Philippines-run islands known as the Kalayaa is to be declared a special tourism zone.

But he says the tourist boats avoid the Second Thomas Shoal and only travel to the islands, reefs and sandbars, which —  for now at least — are less contentious.

"Tourism gives ordinary Filipinos the opportunity to see the real situation and their photos and videos also show the international community what's really happening," he said.

The Code of Conduct is still stalled

Few analysts believe Mr Xi's forces are preparing to seize the Second Thomas Shoal or the other disputed islands anytime soon.

Instead, they say China is seeking to continue so-called "grey zone" tactics to "stop the boats" of other nations using the disputed waters for economic activity.

He said a mutual defence treaty with the United States makes any move on the BRP Sierra Madre a fraught gamble for China.

"I don't think it's a question of landing Chinese troops on there and forcing [people] off the vessel, but clearly China's leaders think they have wiggle room to make life difficult for the resupply missions," he said.

As the clashes continue on the water, Beijing will push on at the ASEAN summit this week with a tortuously slow diplomatic process to negotiate a Code of Conduct for the disputed waters.

After 20 years of talks with ASEAN nations, the code has become a bit of a running joke, despite vows by regional leaders to keep the negotiations going.

"From the view of the frontline states, the Code of Conduct is useless. It's become a way for China to exploit ASEAN's investment in process rather than outcome," Dr Graham said.

Mr Baquisal describes the negotiations as a strategy of "strategic exhaustion" for the Philippines: An effort to tie up political and diplomatic resources while China works to push out Filipino boats from the disputed sea.

Unlike a few of the other states with claims, the Philippines doesn't do any oil or gas extraction, partly because efforts to jointly do it with Chinese and Vietnamese help have faced various hurdles.

Long term, the inability to bring home substantial catches could have a huge economic impact on the coastal communities and food security of the Philippines.

But in the meantime, fisherman like Mr Caberoy are persisting.

"We'll go back out to the West Philippines Sea next month," he said with a toothy grin, using the Philippines' name for the area.

"Because it's our fishing ground."