The Philippines has lodged a formal diplomatic protest against China following the reported appearance of a floating structure within the disputed Scarborough Shoal in the South China Sea, authorities confirmed on Tuesday.

The Philippine Department of Foreign Affairs said it had undertaken appropriate diplomatic action after the installation was detected in waters claimed by Manila as part of its maritime jurisdiction.

According to a government task force monitoring activities in the West Philippine Sea, the structure measured approximately six by six metres and appeared to be fitted with an antenna-like device. It was first observed near the entrance of the lagoon at Scarborough Shoal before later surveillance images showed it deeper inside the atoll’s shallow waters.

Officials said intelligence and monitoring reports indicated that the installation may have been occupied at certain periods, based on images obtained during recent surveillance operations.

The task force reiterated the Philippine government’s commitment to protecting its sovereign rights and maritime interests while responding to developments in accordance with international law.

Defence authorities said they are analysing intelligence reports and satellite imagery to determine the nature, purpose and origin of the structure. Monitoring operations in the area remain ongoing.

Recent satellite photographs reviewed by international observers reportedly showed the structure inside the lagoon, although subsequent images suggested it had later been removed.

Scarborough Shoal, located about 200 kilometres from the Philippine coast, has remained a major flashpoint in the long-running territorial dispute between Manila and Beijing. China has maintained a significant coast guard and maritime presence around the shoal since 2012, leading to recurring diplomatic confrontations between the two countries.

Although a 2016 international arbitral tribunal ruling largely favoured the Philippines in the broader South China Sea dispute, competing claims over Scarborough Shoal remain unresolved, with both nations continuing to assert sovereignty over the strategically important maritime feature.

The latest development is expected to further heighten tensions in the contested waterway, one of the world’s most strategically significant maritime routes.