Major Escalation: Chinese Research Vessel Personnel Land on Sandy Cay 2 and Cay 3 Within Pag-asa Island 12nm Territorial Sea; PCG Aircraft Issues Challenges

China's research vessel Xiang Yang Hong 33, escorted by CCG vessels 5101 and 5309, moved from its previous Reed Bank survey area into the 12-nautical-mile territorial sea of Pag-asa (Thitu) Island — the Philippines' largest occupied Spratly feature — in a significant escalation of the ongoing maritime standoff. Philippine Coast Guard and intelligence monitoring confirmed that Chinese personnel from the Xiang Yang Hong 33 were ferried via rigid-hulled inflatable boats (RHIBs) and rubber boats onto Sandy Cay 2 (Cay-2) and subsequently Sandy Cay 3 (Cay-3), both of which lie within the territorial sea of Pag-asa Island. Philippine Coast Guard aircraft Islander 4177 conducted a maritime domain awareness mission and issued repeated radio challenges demanding the cessation of all activities and the immediate departure of Chinese personnel from the Philippine sandbanks. The challenges were unanswered by the Chinese crew. China's Global Times framed the incident as the PCG aircraft 'harassing' the Chinese research vessel at 'Houteng Jiao' (China's designation for the area) — directly contradicting Philippine accounts of Chinese personnel conducting unauthorized landings on Philippine territory. The escalation is qualitatively different from the Reed Bank phase of the standoff: whereas the Reed Bank presence (May 7–17) constituted an UNCLOS Article 246 violation in the Philippine EEZ, the movement into Pag-asa's 12nm territorial sea and the physical landing of personnel on Philippine sandbars represents a direct challenge to Philippine territorial sovereignty — the first documented Chinese personnel landing on Philippine-claimed Spratly sandbars since modern Philippine monitoring began. The Philippines did not immediately announce any military response to the landing. PCG officially announced an investigation. Sources confirmed the movements were documented via Philippine air reconnaissance.