Only six months after declaring his "separation" with the United States and "realignment" with China, Mr Duterte said the Philippines needs to assert its jurisdiction over areas it claims, a move likely to provoke rival claimants, including China.

"It looks like everybody else is making a grab for the islands there, so we better live on those that are vacant," the President told reporters during a visit to a military camp on the western island of Palawan.

"I have ordered the armed forces to occupy all??? at least, let us get what is ours now and make a strong point there that it is ours."

Since taking office last year Mr Duterte, a foul-mouthed former provincial mayor, has made growing ties with Beijing a priority despite the fact that China has been building military installations and runways on at least seven islands in disputed areas.

Armaments on the islands include surface-to-air missiles.

The Philippine armed forces already deploys troops on nine islands, including Thitu, which is also known as Pag-asa, the second biggest island in the South China Sea that is also claimed by China.

But Philippine defence secretary Delfin Lorenzana told reporters that Mr Duterte now wants his armed forces to build permanent facilities, including barracks, water desalination plants, sewage disposal systems, power generators, light houses and shelters for fishermen.

Mr Duterte said that on Philippine Independence Day in June he may go to Pag-asa island to raise the Philippine flag there.

The island is close to Subi Reef which China has occupied.

Mr Duterte had adopted a non-confrontational approach to China after securing billions of dollars worth of investments from Beijing during a visit there last October.

He has not pursued a ruling from an international tribunal in The Hague that China did not have historic rights in the South China Sea.

In September last year Mr Duterte's national security adviser said he wanted to "demilitarise" the South China Sea to improve chances of a peaceful settlement among rival claimants, which also include Taiwan, Vietnam, Malaysia and Brunei.

Mr Duterte has often made conflicting statements on foreign policy since he was swept into power pledging to wipe out drug use and crime.

US President Donald Trump has so far taken a tough stance on China's claims in the South China Sea, insisting it will defend international interest there.

Much of Australia's trade passes through the area's strategic waterways.