The two neighbours both claim the shoal as part of their territory. But China took control of the ring of reefs just 230km from the main Philippine island of Luzon in 2012 after a standoff with the Philippine navy. “We fear that declaring it as a marine sanctuary would pave way for another fishing blockade,” Fernando Hicap, chairman of fishermen support group Pamalakaya, said in a statement. “This time it will be our own law and government that will prohibit [Filipino fishermen], not China,” he added.

A spokesperson for Duterte told AFP on Wednesday his office would soon release an executive order on the new “no-fishing zone” for both Filipinos and Chinese fishermen. “This would be subject to friendly negotiations so we won’t create friction with other claimants,” said Ana Marie Banaag, presidential communications assistant secretary.

Chinese foreign ministry spokesperson Geng Shuang on Tuesday had no comment on Duterte’s declaration but said Beijing had made “proper arrangements for fishing activities”.

However Filipino fishermen told AFP the Duterte plan would hurt their livelihood. “We are against that because it is inside the lagoon where there is more catch,” said Charlito Maniago, village captain in Infanta, one of the main Scarborough Shoal fishing towns on Luzon.

Maritime law expert Jay Batongbacal said Duterte’s declaration favoured China since the Philippines could further lose access to the shoal. “China could just as easily accept the Philippine move and not act in return, because they derive the benefit anyway,” Batongbacal said in a statement.