The coastguard of the Philippines urged the country's fishermen on Wednesday to keep operating at the disputed Scarborough Shoal and other sites in the South China Sea, pledging to step up patrols there despite an imposing Chinese presence.

Philippine vessels were unable to maintain a constant presence but were committed to protecting the rights of fishermen inside the country's exclusive economic zone (EEZ), coastguard spokesperson Commodore Jay Tarriela said.

"We're going to increase patrols in Bajo de Masinloc and other areas where Filipino fishermen are," he told DZRH radio, referring to the shoal, one of Asia's most contested maritime features, by its Philippine name.

On Monday, the coastguard cut a 300-m (980-ft) floating barrier installed by China that blocked access to the Scarborough Shoal, a bold response in an area Beijing has controlled for more than a decade with coastguard ships and a fleet of large fishing vessels.

China's response has been measured, with its foreign ministry advising Manila on Tuesday to avoid provocations and not cause trouble.

Defence Secretary Gilbert Teodoro said the Philippines' cutting of the cordon was not a provocation.

"We are reacting to their action," he said during a senate hearing on Wednesday. "They moved first, they blocked our fishers."

The rocky, mid-sea outcrop is the site of numerous diplomatic rows. Both countries claim sovereignty over the shoal, a prime fishing spot about 200 km (124 miles) off the Philippines and 850 km (530 miles) from mainland China and its southern island of Hainan.

Close to shipping lanes that transport an estimated $3.4 trillion of annual commerce, control of the shoal is strategic for Beijing, which claims sovereignty over most of the South China Sea.

Those claims complicate fisheries and offshore oil and gas activities by its Southeast Asian neighbours, however.

Tarriela said the Philippine fisheries bureau had successfully anchored a vessel just 300 m (980 ft) from the Scarborough Shoal's lagoon, its closest point to the atoll since China seized it in 2012.

It is unclear whether China's use of a barrier represents a change to a status quo that has existed since 2017 in which Beijing's coastguard allowed Filipinos to operate there, albeit on a far smaller scale than China.

It comes amid soured relations, with the Philippines increasingly assertive over the conduct of China's coastguard in its EEZ, as it strengthens military ties with ally the United States by expanding access to its bases.

"The Scarborough Shoal is closer to the Philippines," said fisherman Pepito Fabros who had come ashore in the province of Zambales between trips to sea.

"Why are they stopping us from entering?"