Updated

The Philippine defense and military chiefs visited a Philippine-occupied island in the disputed South China Sea on Friday and announced that the construction of facilities will start soon there, a move likely to infuriate rival claimant China, which is believed to have put missiles on its man-made islands nearby.

The aircraft that took Defense Secretary Delfin Lorenzana, military chief of staff Gen. Eduardo Ano and about 40 journalists to Pag-asa Island, known internationally as Thitu, were challenged by China as they flew in the vicinity of Chinese-held Subi Reef, Lorenzana said.

He said Filipino pilots always reply that they are flying over Philippine territory, after they were warned by Chinese personnel that they were entering the periphery of Chinese installations and told to avoid miscalculation.

China claims virtually the entire sea and has aggressively tried to fortify its foothold by constructing seven island outposts, some with runways and radars and more recently weapons systems, to the consternation of other claimants and the United States, which insists on freedom of navigation in international waters.

Philippine security officials also said they were checking reports that Filipino fishermen were harassed by the Chinese coast guard near Union Bank in the South China Sea few days ago. Lorenzana said authorities have yet to get the fishermen's statements, but if true, the Philippines would file a diplomatic protest with China.

President Rodrigo Duterte has said China dissuaded him from flying to the island to raise his country's flag when the Philippines celebrates its Independence Day on June 12.

"So because of our friendship with China and because we value your friendship, we will not, I will not go there to raise the Philippine flag," he said in a speech last week in Saudi Arabia. He said he may send his son instead.

Lorenzana told troops after a flag-raising ceremony that Duterte had instructed him to inspect the island and see to it that facilities are built there as soon as possible. They include a beaching ramp, which is expected to be finished by July so ships can bring materials for the repair and lengthening of the 1.2 kilometer (0.75 mile)-long runway to allow more flights and improve safety.

He said that 1.6 billion pesos ($32 million) has been earmarked for construction on Pag-asa alone to include a fish port, solar power, water desalination plant, improved housing for soldiers, and facilities for marine research and tourists.

The government also plans to fortify small buildings on eight much smaller reefs and atolls occupied by Filipino forces.

Lorenzana said China could be expected to protest the construction. The two countries, as well as the other five claimants, regularly exchange such protests. But Lorenzana said the dispute is being managed through dialogue and he did not expect any untoward incident.

"This is just a normal visit within our territory," he told reporters. "We are just visiting our territory to look at the conditions of our people here."

He said China and Vietnam have already fortified islands they occupy and the Philippines was the only one that has not yet done so, even though Filipino troops have been stationed on Pag-asa since the late 1960s.

"We should have done this before," he added.

The latest visit may highlight the territorial disputes when Duterte hosts an annual regional summit in Manila next week. China won't attend as it is not a member of the Association of Southeast Asian Nations, but a wider regional summit is scheduled in November that includes both China and the U.S.