Nearly 18,000 troops are taking part in the annual exercises dubbed Balikatan, or "shoulder to shoulder" in Filipino, which for the first time will include a live-fire drill in the South China Sea, which Beijing claims almost entirely.

The drills follow Monday's conclusion of a three-day Chinese military exercise that simulated targeted strikes and a blockade of self-ruled, democratic Taiwan, which Beijing considers part of its territory.

Balikatan will include military helicopters landing on a Philippine island off the northern tip of the main island of Luzon, nearly 300 kilometres (180 miles) from Taiwan, and the retaking of another island by amphibious forces.

It will be the first time the exercises have been held under President Ferdinand Marcos, who has sought to strengthen ties with the United States after his predecessor Rodrigo Duterte trashed the alliance.

"In order for us to protect our sovereign territory, we really have to drill and exercise how we are going to retake an island that's been taken away from us," Philippine exercises spokesman Colonel Michael Logico told reporters after the opening ceremony at a military camp in Manila.

In recent months, Manila and Washington have agreed to restart joint maritime patrols in the South China Sea and struck a deal to expand the US forces' footprint in the Philippines, which has infuriated China.

US troops will be allowed to use an additional four Philippine military bases under the pact, including a naval base not far from Taiwan.

The Philippines' proximity to the island could potentially make it a key US partner in the event of a Chinese invasion.

At a joint news conference Tuesday, both armies did not address questions about the Taiwan tensions and a possible role for the Philippines if China invaded Taiwan.

News of the expanded base access had prompted China to accuse the United States of "endangering regional peace and stability".

"Countries in this part of the world must uphold strategic independence and firmly resist the Cold-War mentality and bloc confrontation," China's ambassador to Manila, Huang Xilian, said last week.

- Boosting military tactics -

About 12,200 American, 5,400 Filipino and just over 100 Australian soldiers will participate in the two weeks of Balikatan exercises -- about twice as many as last year.

About 50 leftwing protesters staged a rally outside the opening ceremony venue, calling on the Philippine government to scrap the exercises.

As part of the exercises, troops will stage an amphibious landing on the western island of Palawan, the closest Philippine landmass to the Spratly Islands, where Beijing and Manila have rival claims.

The Americans will also use their Patriot missiles, considered one of the best air defence systems in the world, and the HIMARS precision rocket system, which has helped Ukrainian forces fighting the Russian invaders.

The two armies originally planned to fire live rounds at sea off the northern province of Ilocos Norte, about 355 kilometres from Taiwan's south coast, but later on had to move it further down the South China Sea, Philippine Army Major-General Marvin Licudine said.

The original site was "not sufficiently prepared" for unloading the needed equipment, he added.

The new venue is less than 300 kilometres east of the Chinese-held Scarborough Shoal.

The exercises will enhance "tactics, techniques and procedures across a wide range of military operations," said Philippine military spokesman Colonel Medel Aguilar.

Soon after the opening ceremony in Manila, the Philippine defence and foreign ministers will jointly meet their US counterparts in Washington.