The Philippines said Monday it would protest to China about what it called Beijing's increasing patrols in a disputed area of the South China Sea believed to hold vast oil and gas resources.

Foreign Department spokesman Charles Jose announced the protest a day after the airing of a television interview in which President Benigno Aquino raised the alarm over the Chinese vessels at Reed Bank.

"The frequent passage of Chinese vessels in Recto Bank is not an innocent exercise of freedom of navigation but is actually done as part of a pattern of illegitimate sovereign patrol in the Philippines' exclusive economic zone, pursuant to China's unilateral effort to change the status quo in the South China Sea," Jose told reporters, referring to Reed Bank by its Filipino name.

He said Reed Bank was about 85 nautical miles (157 kilometres) from the western Philippine island of Palawan, making it well within the country's internationally-recognised exclusive economic zone.

In contrast, Jose said the bank was 595 nautical miles from the coast of China's Hainan island.

A day earlier, Aquino expressed concern at the presence of Chinese government ships in the disputed waters, questioning how far China intended to push its claims.

In an interview with ABC-5 television network, transcripts of which were released by the presidential palace, Aquino said: "They want to claim what is ours. How far will we let this go? Are we going to be content to just tell them, 'Okay, you can go this far'"?

"What are they doing there? What studies are they doing? Hopefully this will not add to the tensions between the two of us," Aquino said.

Defence Department spokesman Peter Paul Galvez said Monday the ships were "hydrological research vessels" capable of mapping the ocean floor, adding they were first sighted in June but could remain at sea for over a month.

China lays claim to almost all of the South China Sea, even up to the coasts of its neighbours. This conflicts with the territorial claims of the Philippines as well as Brunei, Malaysia, Taiwan and Vietnam.

In recent years, tensions between the Philippines and China have risen as China has aggressively pressed its claim, citing "historical facts" and occupying and fortifying outcrops and islets.

Aquino joked that China could eventually claim all of the Philippines, citing the presence of Chinese migrants in Manila as early as the 16th century when the archipelago was a Spanish colony.

Aquino's spokesman Herminio Coloma said Monday the Philippines would continue to rely mainly on a "strategy of finding a peaceful and diplomatic solution" to the South China Sea dispute.

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