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MANILA - President Rodrigo Duterte may be impeached if he fails to protect the country's territory in the West Philippine Sea, a former solicitor general said Tuesday.

Speaking to ANC, lawyer Florin Hilbay said Duterte took an oath to protect and defend the Constitution.

"If the President commits culpable violation of the Constitution, if the President reneges on his promise to protect national territory, that is a clear betrayal of public trust," he said.

US network CNBC reported earlier that the Chinese army had installed anti-ship and air-to-air defenses on outposts also claimed by Vietnam and the Philippines over the last 30 days.

Duterte has not called out China over the reported missile deployment but instead blamed the US and former President Benigno Aquino III for their supposed failure to stop China's militarization in the area.

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Hilbay said the Duterte administration's policy of "total friendliness" with China is not working as the Asian economic giant has reportedly succeeded in militarizing its artificial islands.

"We are now realizing the fruition of a century-long plan of China which is to take effective control of the South China Sea, including the West Philippine Sea," he said.

He said the Philippines need to formally protest China's moves and implement a plan that does not change every time a new administration takes over the government.

"We are clearly seeing the disappointing turn of events that is anchored on the President's policy of basically giving everything to China," the lawyer said.

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Hilbay said it is not too late to implement a multilateral approach in dealing with China and invoking the arbitral ruling that says the West Philippine Sea is part of the Philippines' territory.