Manila accuses Chinese vessels of harassing and blocking Philippine boats delivering food, water and materials for badly needed repairs.
Beijing, which has urged Manila to remove the ship, insists the Philippine vessels are infringing China’s territorial sovereignty.
Second Thomas Shoal is about 200km from the western Philippine island of Palawan, and more than 1,000km from China’s nearest major landmass, Hainan island.
On Friday, the Philippines accused the Chinese coast guard of “dangerous harassment” of Filipino boats near the reef, including firing a water cannon and blocking vessels.
The incident happened nearly three weeks after two collisions between Chinese and Philippine vessels during another resupply mission, with the countries trading blame.
“SHOULDER-TO-SHOULDER”
China’s actions have sparked international concern and fueled fears for a potential accident or miscalculation serious enough to ignite a military conflict.
Manila’s longtime ally Washington reiterated Friday that its mutual defence pact with the Philippines “extends to armed attacks on Philippine armed forces, public vessels, or aircraft – including those of its Coast Guard – anywhere in the South China Sea”.
“The United States stands shoulder-to-shoulder with our Philippine ally in the face of the People’s Republic of China’s (PRC) repeated harassment in the South China Sea,” US State Department spokesman Matthew Miller said in a statement.