Philippines President Ferdinand Marcos Jr. said on Wednesday new rules outlined by China's coast guard that could result in the detention of foreigners in the South China Sea were an escalation and "worrisome."

China, which has maritime sovereignty disputes with the Philippines and other claimant countries, has issued new rules effective June 15 that would enforce a 2021 coast guard law and allow detention of foreigners suspected of trespassing.

China routinely accuses vessels of trespassing in areas of the South China Sea that fall inside the exclusive economic zones of its neighbors and has clashed repeatedly with the Philippines in the past year.

"The new policy of threatening to detain our own citizens, that is different. That is an escalation of the situation," Marcos told reporters while on a state visit in Brunei.

The Philippines "will use any point of contact with China to stop aggressive actions" and allow Filipino fishermen to fish in the South China Sea, Marcos said.

If aggressive actions are managed, Marcos said, "then we can go all about our business in a peaceful way."

Marcos has taken a tougher line than his predecessor over China's actions in the South China Sea, emboldened by support from defense ally the United States, as well as Japan and Australia.

China's Embassy in Manila did not immediately respond to a request for comment.

Beijing claims jurisdiction over most of the South China Sea, a conduit for more than $3 trillion in annual ship-borne trade.

In 2016, an international arbitral tribunal said China's vast claims had no basis under international law, a decision Beijing has rejected. China insists historic records and old maps make clear it has sovereignty over most of the sea and many islands there.