MANILA (REUTERS) - The Philippines will beef up its naval presence in the South China Sea to protect its fishermen, its new military chief said, as concerns grow about the operations of China's coastguard in disputed waters.

The move comes after the Philippines protested a new law in China that allows its coastguard to board or open fire on foreign vessels in waters it regards as its territory, which officials said could heighten risks of a miscalculation.

"We will increase our visibility through the deployment of more naval assets, but I just want to make clear our navy presence there is not (to) wage war against China but to secure our own people," Lieutenant-General Cirilito Sobejana said in a media briefing on Tuesday (Feb 9).

China claims about 90 per cent of the South China Sea as its own and deploys its coastguard throughout the strategically important waterway. Those are often accompanied by large numbers of fishing boats seen widely as a Chinese maritime militia, which other claimants accuse of harassing their fishermen.

"That pronouncement by China that their coastguard can open fire at people intruding into their territory is very alarming," Lt-Gen Sobejana said.

"It's a very irresponsible statement because our people are not going to the disputed area to go to war but to earn a living."

China's embassy in Manila did not immediately respond to a request for comment on the general's remarks.

The Philippines, however, has very limited naval capabilities compared with China's fleet of navy and coastguard.

US Secretary of State Antony Blinken last month stressed the importance of a defence pact with Manila and its clear application if the Philippines came under attack.

The United States has held regular patrols in disputed areas of the South China Sea to underline its presence in the region, the latest on Tuesday, when two US carrier groups conducted joint exercises.