China's People's Liberation Army (PLA) Southern Theater Command said it had "organised naval and air forces to conduct routine patrols" in the sea from January 3 to 4.
The United States meanwhile announced that a carrier strike group led by the USS Carl Vinson was conducting two days of drills with the Philippine Navy.
"The US Navy regularly conducts exercises like these to strengthen ties among allied and partner nations," a statement said.
The moves come after videos released by the Philippine Coast Guard last month showed Chinese ships blasting water at Philippine boats. There was also recently a collision between Philippine and Chinese boats at a flashpoint reef, with both countries trading blame.
The PLA 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 PLA statement said.
"They remain fully aware of any military activities that disrupt the South China Sea and create flashpoints."
Beijing has criticised a more aggressive Philippine policy in the area and warned Manila to "make the rational choice" in response to recent incidents.
Philippine President Ferdinand Marcos has vowed not to give in to "coercion", without mentioning China by name.
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