Thitu Island, known as Pag-asa in the Philippines, is home to about 400 Filipinos, mostly fishermen and their families, who China accuse of living there illegally.

It lies about 450 kilometres (280 miles) west of Palawan within the disputed Spratly island chain, a group of more than 700 islets, reefs and atolls believed to sit above vast natural resources.

Senator Risa Hontiveros, an outspoken critic of China, told AFP on Saturday she believed Filipinos were not ready to give up "any portion of the West Philippine Sea", using Manila's favoured term for the waters off its western seaboard.

"We need continuous diplomatic and political pushback," Hontiveros said after a plane journey of more than two hours with local journalists.

While welcoming the strengthening of the Philippines' treaty relationship with the United States in recent years, Hontiveros said Manila hoped to bring even more "like-minded nations" into the fold.

"We need to continuously develop our security and defence relations with (other countries), including joint patrols," she said.

An AFP journalist who flew to Thitu Island aboard a second plane saw Chinese navy and coast guard vessels patrolling near the island.

Hontiveros, who noted that symbols on her cell phone screen changed to Chinese characters before landing, said she was bringing with her essential goods and medical services to help the island's development.

The Chinese Embassy in Manila did not respond immediately to a request for comment.

Hontiveros's trip comes days after Vice President Sara Duterte announced her candidacy for the 2028 presidential election.

Her father, former president Rodrigo Duterte, who is facing an International Criminal Court trial on charges of crimes against humanity, attempted a more conciliatory approach with China.

Critics say his efforts yielded few meaningful concessions.

Hontiveros, who told AFP she was open to a presidential run herself, said she believed Sara Duterte would likely adopt a similarly China-friendly approach if elected president.

Asked about the possibility of a US-China conflict over neighbouring Taiwan, she said the Philippines should be "very concerned", noting the proximity of its northernmost Batanes chain to the self-ruled island.

China claims Taiwan as part of its territory and has threatened to use force to bring it under its control.

"We have a lot of countrymen working there," Hontiveros said. "All the more that we should be proactive to... insist on a peaceful resolution of conflicts."