As a U.S. Navy surveillance plane flew in circles, keeping a close watch, dozens of Chinese coast guard and accompanying ships chased and encircled Philippine vessels in the latest confrontation in one of the most dangerous flashpoints in the South China Sea.

At the height of Friday’s four-hour faceoff in the high seas, a Chinese coast guard ship blasted a water cannon toward a Philippine motorboat delivering food and other supplies to Filipino forces on a marooned, rusting warship that serves as the country’s fragile territorial outpost at Second Thomas Shoal.

China has steadfastly stood by its claim to virtually the entire strategic waterway, clashing with its smaller neighbors and drawing in the United States, Manila’s treaty ally and China’s main rival in the Asia-Pacific region. Washington and its allies have deployed navy ships and fighter aircraft to promote freedom of navigation and overflight, build up deterrence and reassure allies like the Philippines.