Beijing has sought to expand its presence in the disputed waterway for years, brushing aside an international ruling that its claim to most of the sea has no legal basis.

In recent months, China has deployed navy, coast guard and so-called maritime militia forces -- allegedly Chinese fishing vessels -- in a bid to bar the Philippines from a trio of strategically important reefs and islands in the South China Sea.

"We need to have a persistent presence in the West Philippine Sea," Rear Admiral Roy Vincent Trinidad told a security conference, adding outlying areas of the Philippine archipelago need to be connected to the "entire country".

Trinidad, the navy's spokesman for South China Sea issues, said that all Filipinos must "understand the existential threat", stressing the process could take years.

In the meantime, "we are capitalising (on) like-minded navies, like-minded nations, our partners and allies and friends", he said, naming Australia, New Zealand, Japan, Vietnam, Canada, the US, Britain, and France.

He made the comments as some 3,000 Philippine troops began earlier this week 12 days of manoeuvres in the South China Sea and adjacent islands.

"We will be having island seizure exercises, amphibious counter-landing exercises and air defence exercises," Colonel Michael Logico, an exercise organiser, told reporters at the start of the war games on Monday.

Elaborating on his speech, Trinidad later told reporters that joint patrols, dubbed Multilateral Maritime Cooperative Activity (MMCA), have reined in Chinese conduct at sea.

"During the conduct of MMCAs, there have been no observed coercive and aggressive actions by the (People's Liberation Army) Navy, Coast Guard or the maritime militia," he said.

The lull was observed for "a few days before and during, and a few days after" the exercises, he said.

Violent encounters with Chinese vessels typically occur during Philippine resupply missions to its remote garrisons in the area.

In Beijing, foreign ministry spokeswoman Mao Ning stressed "China has sovereignty over the South China Sea islands and their adjacent waters" and "we safeguard our sovereign rights and interests in accordance with domestic and international law".

She added: "Making a show of force and provoking confrontation in the South China Sea will only escalate tensions and undermine regional stability."

While Washington and its allies have avoided taking sides in the territorial dispute, they say Chinese actions threaten freedom of navigation essential for trade, with trillions of dollars passing through the waterway each year.