ABOARD BRP CABRA (AP) — As a U.S. Navy plane circled overhead, two Philippine boats breached a Chinese coast guard blockade in a dangerous confrontation in the disputed South China Sea to deliver food and other supplies to Filipino forces guarding a contested shoal.

Two Philippine coast guard vessels escorting the supply boats, however, were blocked by at least four Chinese coast guard ships for about five hours Tuesday in a tense standoff off Second Thomas Shoal.

The dangerous encounter is the latest flare-up from the long-seething territorial disputes in the busy sea that involve China, the Philippines, Vietnam, Malaysia, Taiwan and Brunei. It’s regarded as an Asian flashpoint and has become a delicate fault line in the US-China rivalry.

The Philippine coast guard invited a small group of journalists, including two from The Associated Press, to join its ships that secured the supply boats as part of a new strategy aimed at exposing China’s increasingly aggressive actions in the South China Sea, which Beijing claims virtually in its entirety.

The Cabra and another coast guard ship, the BRP Sindangan, were forced to stop, surrounded by four Chinese coast guard ships and four suspected militia vessels, as the two boats delivered supplies to the Filipino forces at Second Thomas Shoal, more than 7 kilometers (4 miles) away.

All the Philippine vessels sailed away without further incident after the supplies and a fresh crew of Filipino sailors were delivered to the military outpost on a long-marooned Philippine navy ship at the shoal.

“We’re happy that the resupply mission succeeded despite all the dangerous blockings and other actions,” Cmdr. Emmanuel Dangate of the Cabra told AP.

Coast Guard spokesperson Commodore Jay Tarriela condemned the Chinese coast guard blockade and other perilous maneuvers as a violation of international regulations aimed at avoiding sea collisions. The coast guard would provide a report to the Department of Foreign Affairs in Manila for a possible diplomatic protest against China, he said.

The United States lays no claim to the South China Sea but has declared that freedom of navigation and flight and peacefully resolving disputes are in its national interest.

After a Chinese coast guard ship used a water cannon against a Philippine supply boat on Aug. 5, Washington renewed a warning that it’s obligated to defend its longtime treaty ally if Filipino forces, aircraft and vessels come under an armed attack, including in the South China Sea.