China conducted military "combat patrols" Sunday in the disputed South China Sea, its army said, the same day as joint drills by the Philippines, the United States, Japan and Australia.

The announcement comes one day after defence chiefs from four countries including the Philippines -- which has been engaged in several contentious maritime disputes with Beijing recently -- said they would conduct joint drills Sunday in the area.

Beijing's People's Liberation Army (PLA) Southern Theater Command said it was organsing "joint naval and air combat patrols in the South China Sea".

"All military activities that mess up the situation in the South China Sea and create hotspots are under control," it said in a statement, in an apparent swipe at the other drills being held in the waters.

Further details about the Chinese military activities in the waterway Sunday were not announced.

The exercises take place days before US President Joe Biden is due to hold the first trilateral summit with the leaders of the Philippines and Japan.

Top US officials have repeatedly declared the United States' "ironclad" commitment to defending the Philippines against an armed attack in the South China Sea -- to the consternation of Beijing.

China claims territorial sovereignty over nearly all of the South China Sea and has been increasingly assertive in the region in recent years.

China's Coast Guard said Saturday it had "handled" a situation on Thursday at a disputed reef where several ships from the Philippines were engaged in "illegal" operations.

"Under the guise of 'protecting fishing', Philippine government ships have illegally violated and provoked, organised media to deliberately incite and mislead, continuing to undermine stability in the South China Sea," spokesman Gan Yu said.

"We are telling the Philippines that any infringement tactics are in vain," Gan said, adding that China would "regularly enforce the law in waters under (its) jurisdiction".

Beijing has brushed aside competing territorial claims by several Southeast Asian countries in the South China Sea -- a crucial route for global trade -- as well as an international ruling that declared its stance baseless.

The drills conducted Sunday by the Philippines, United States, Japan and Australia are intended to "(ensure) that all countries are free to fly, sail, and operate wherever international law allows," US Defense Secretary Lloyd Austin said in a joint statement.

Named the "Maritime Cooperative Activity", the drills will include naval and air force units from all four countries, the joint statement said.

There were no details in the statement on what the drills would precisely include.

The Japanese embassy in Manila said in a statement that "anti-submarine warfare training" would be included in the drills.

Last week, Australian warship HMAS Warramunga arrived at the Philippine island of Palawan, which faces the hotly contested waters.

Philippine President Ferdinand Marcos issued a strongly worded statement on March 28, vowing the country would not be "cowed into silence, submission, or subservience" by China.

Talks between the Philippines and Japan for a defence pact that would allow the countries to deploy troops on each other's territory were "still ongoing", a spokesman for the Philippine foreign affairs department told reporters last week.

Manila already has a similar agreement with Australia and the United States.