The move is a symbolic and assertive display of sovereignty over the contested, triangle-shaped reef in the busy South China Sea waterway. While both countries lay claim to the shoal, it has been under Beijing's de facto control since 2012.
A video posted on Douyin, the Chinese version of TikTok, showed uniformed coast guard officers standing in formation on the aft deck of the patrol ship Dahao (CCG 3304), saluting as the Chinese national flag was raised.
A caption on the video read: "We guard this blue territory, assuring the nation of our unwavering commitment."
The Philippine Coast Guard did not immediately respond to a request for comment from Reuters on Wednesday.
A History of Confrontation
China seized control of Scarborough Shoal in 2012 after a tense maritime standoff with the Philippines and has maintained a constant presence of coast guard and fishing vessels there ever since.
The shoal has been the site of numerous flare-ups in recent years. The Philippines has repeatedly accused the China Coast Guard of using aggressive tactics, including firing water cannons at Philippine vessels, ramming boats, and performing dangerous maneuvers in close proximity. Chinese jets have also been reported tailing Philippine aircraft flying over the atoll. Both sides routinely accuse each other of provocation and encroachment, though no clashes have escalated into armed conflict.
A landmark 2016 ruling by the Permanent Court of Arbitration in The Hague largely favored the Philippines in the broader South China Sea dispute. While the ruling did not decide on the sovereignty of Scarborough Shoal, it did declare that Beijing's blockade of the area violated international law, as it is a traditional fishing ground for several nations, including the Philippines and Vietnam.
Tensions were further inflamed in September when China announced plans to establish a "national" nature reserve at the shoal, a move that drew sharp condemnation from Manila.
The specific vessel used in the ceremony, CCG 3304, has been the subject of previous diplomatic protests from the Philippines for its "illegal presence" at the shoal. The atoll is known as Huangyan Island in China, while in the Philippines, it is called Panatag Shoal.