China conducted "combat patrols" Sunday in the South China Sea, its army said, the same day the Philippines, the United States, Japan and Australia held their first joint drills in the disputed waters.

A photo handout from the Armed Forces of the Philippines of the first Multilateral Maritime Cooperative Activity between the Philippines, the United States, Australia and Japan, in South China Sea.

The maritime activities took place days before US President Joe Biden was due to hold the first trilateral summit with the leaders of the Philippines and Japan, with growing tensions over the hotly contested South China Sea on the agenda.

Beijing's People's Liberation Army (PLA) Southern Theater Command said it was organising "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.

The Philippine military said its drills with the United States, Australia and Japan "demonstrated the participating countries' commitment to strengthen regional and international cooperation in support of a free and open Indo-Pacific through interoperability exercises in the maritime domain."

Dubbed the "Multilateral Maritime Cooperative Activity", the drills included naval and air force units from all four countries.

They performed a communication exercise, division tactics, and a photo exercise, the Philippine statement said Sunday.

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

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

- 'Ironclad' -

The United States has sought to strengthen defence cooperation with its allies in the region to counter China's growing influence.

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

China claims nearly all of the waterway despite competing claims from other countries, including the Philippines, and an international ruling that its stance has no legal basis.

China's Coast Guard said Saturday it had "handled" a situation at a disputed reef on Thursday, when it claimed 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".

Relations between Manila and Beijing have deteriorated under Philippine President Ferdinand Marcos, who has taken a stronger stance than his predecessor Rodrigo Duterte against Chinese actions in the sea.

There have been several confrontations between Philippine and Chinese vessels near contested reefs in recent months, including collisions.

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

He also said the Philippines would respond to recent incidents with countermeasures that would be "proportionate, deliberate, and reasonable".