The People's Liberation Army's Southern Theater Command said it had "organised naval and air forces to conduct routine patrols" in the sea from January 3 to 4.

The statement did not mention where exactly the patrols would take place or give specific details of their aims.

Beijing claims almost the entire South China Sea and has ignored an international tribunal ruling that its assertions have no legal basis.

It deploys boats to patrol the busy waterway and has built artificial islands that it has militarised to reinforce its claims.

"Troops in the theater remain on high alert at all times to resolutely safeguard national sovereignty, security and maritime rights and interests," the statement said.

"They remain fully aware of any military activities that disrupt the South China Sea and create flashpoints."

Tensions between China and the Philippines have risen in recent weeks as vessels from both countries have clashed in the contested waters.

Beijing has blamed a more aggressive Philippine policy and warned Manila to "make the rational choice" in response to the incidents.

Philippine President Ferdinand Marcos has vowed not to give in to "coercion", without mentioning China by name.