China revealed plans a day earlier for a reserve to maintain "diversity, stability, and sustainability of the natural ecosystem of Huangyan Island", Beijing's name for the contested chain of reefs.

Chinese state media said the reserve would cover an area of 3,523.67 hectares (8,707 acres), with its "primary focus" being the coral reef ecosystem.

"The Philippines strongly protests the recent approval by the State Council of China of the establishment of the so-called 'Huangyan Island National Nature Reserve,'" the foreign affairs department said in a statement.

"The Philippines will be issuing a formal diplomatic protest against this illegitimate and unlawful action by China," it said, adding it held sovereignty over the area in question.

Scarborough Shoal lies 240 kilometres (150 miles) west of the Philippines' main island of Luzon and nearly 900 kilometres from Hainan, the nearest major Chinese land mass.

Last month, a Chinese navy vessel collided with one from its own coast guard while chasing a Philippine patrol boat near Scarborough, with Manila releasing dramatic video footage of the confrontation.

And in May, the Philippines slammed what it termed a "high-risk" manoeuvre by a Chinese vessel in the same area. China responded by accusing Manila of sending a ship to "intrude" into its territorial waters.

China claims almost the entirety of the South China Sea, through which more than 60 percent of global maritime trade passes, despite a 2016 court ruling that said its claims had no basis in international law.

The Chinese Embassy in Manila did not immediately respond to a request for comment.