Beijing has said it was conducting air and naval patrols around a contested shoal in the South China Sea to "resolutely defend" its national sovereignty.

The "combat readiness patrols" were to strengthen "vigilance in the sea and air space around the territorial areas of Huangyan Dao," Chinese military's Southern Theatre Command said in a statement on Thursday, using the Chinese name for Scarborough Shoal.

China has organised air and naval forces throughout November, the statement added.

Beijing claims the waters around Scarborough Shoal a chain of reefs that it seized from the Philippines in 2012.

The triangular chain of reefs and rocks is 240 kilometres west of the Philippines' main island of Luzon and nearly 900 kilometres from the nearest major Chinese land mass of Hainan.

Philippine and Chinese vessels have clashed frequently in the past year, resulting in injuries and damages.

Escalating tensions

Tensions escalated in November when Philippine President Ferdinand Marcos signed two laws defining the country's sea waters and imposing fixed lanes for foreign ships.

That sparked a sharp riposte by China, which summoned Manila's envoy "to lodge solemn representations" over their passage.

China's coast guard also vowed to "continue to strengthen patrols and law enforcement in the territorial sea of Scarborough Shoal and relevant waters."

Tensions rose again earlier this month when the United States and the Philippines signed a security agreement that allows the two sides to share classified information.

On Thursday, responding to a question on that security agreement, a spokesperson for China's defence ministry said: "Forming cliques will only exacerbate tensions and undermine regional stability."

"We will continue to take all necessary measures to counter infringement and provocation and firmly safeguard peace and stability in the South China Sea," Wu Qian told a press conference.