SOUTH CHINA SEA, undefined — Sailors aboard two Philippine Coast Guard boats crashed through West Philippine Sea waves, shadowed by Chinese vessels as they attempted to bring desperately needed supplies to colleagues holed up on a ship inside a remote ring of reefs.
The coast guard's BRP Teresa Magbanua has been anchored inside Sabina Shoal since April to assert Manila's claims to the area off its coast and prevent China from seizing it.
But the Filipino sailors on board the ship are running critically low on food and other provisions -- which Monday's tense "humanitarian" mission by two smaller coast guard boats was intended to supply.
Philippine and Chinese vessels have collided twice this month near Sabina Shoal, located 140 kilometers (86 miles) from the Philippines' western island of Palawan and 1,200 kilometers from China's nearest major landmass Hainan island.
AFP journalists on board one of the 44-meter (144-foot) Philippine resupply boats watched as Chinese coast guard and navy ships shadowed both vessels for hours, eventually surrounding them.
With 40 Chinese ships in their path in rough seas, the Philippine Coast Guard turned back, leaving the sailors on the 97-meter Teresa Magbanua without fresh provisions.
Flashpoint fears
Sabina Shoal is the latest reef to become a flashpoint in decades of maritime disputes between the Philippines and China.
In 1995, Beijing began building structures on Mischief Reef, which Manila claims as part of its continental shelf, and China has since constructed several artificial islands that it uses as military outposts.
More recently, the focus of clashes between Philippine and Chinese vessels has been Second Thomas Shoal, about 30 kilometers southeast of Mischief Reef.
A handful of Filipino troops are stationed on a rusty navy ship that the Philippines deliberately grounded there in 1999 to check China's advance.
A Filipino sailor lost a thumb in a clash there in June, when Chinese coast guard members wielding knives, sticks and an axe foiled a Philippine Navy attempt to resupply its troops.
Beijing and Manila reached a "provisional arrangement" in July for the delivery of necessities and rotation of Filipino troops at Second Thomas Shoal.
But now the Philippines faces a new challenge in reaching its coast guard personnel at Sabina Shoal, 60 kilometers east of Second Thomas Shoal.
Sabina Shoal is also the rendezvous point for Philippine resupply missions to Second Thomas Shoal.
"If we lose Escoda Shoal, that would be very easy for China... to prevent our resupply operation that we intend to carry out in Ayungin Shoal because they can basically block it on both sides," Commodore Jay Tarriela, a spokesman for the Philippine Coast Guard, told reporters on Tuesday, using the Filipino names for Sabina and Second Thomas shoals.
'We're not going to withdraw'
Beijing claims almost the entire South China Sea, despite an international ruling that its assertion has no legal basis, and defends its actions against Philippine vessels as lawful and proportional.
Analysts say Beijing's aim is to further encroach on Sabina Shoal, moving deeper into Manila's exclusive economic zone and normalising Chinese control of the area.
The discovery earlier this year of piles of crushed coral at Sabina Shoal ignited suspicion in Manila that Beijing was planning to build another permanent base there, which would be its closest outpost to the Philippine archipelago.
Beijing is using a "salami-slicing strategy", said Don McLain Gill of De La Salle University in Manila, deploying ships to Sabina Shoal and other areas to "stretch" the Philippines' limited maritime resources.
Sabina Shoal's proximity to Palawan is a concern, said Andrea Wong, non-resident research fellow at the Institute for Indo-Pacific Affairs in New Zealand.
"If China gained access to it, it's a matter of time before they can, not invade Palawan per se, but they can also get resources in that area," Wong said, referring to fish stocks and potential oil and gas deposits.
To head off any attempt by China to seize Sabina Shoal, the Philippines sent the Teresa Magbanua there to monitor Chinese activities.
China responded by deploying more vessels, including a 165-meter coast guard vessel.
The situation has echoes of 2012, when Beijing took control of Scarborough Shoal, another strategic feature about 240 kilometers west of the Philippines' main island of Luzon.
Tarriela said lessons had been learned from that incident.
"We were not able to go back the moment we left Bajo de Masinloc," Tarriela said, using the Filipino name for the shoal.
"The Commandant of the Philippine Coast Guard has made it very clear. We're not going to withdraw our forces that would allow China to permanently occupy (Sabina)."