The Philippine military on Thursday accused China of sending more ships to a disputed shoal in the South China Sea, describing the move as an insult that would further inflame tensions.

Four Chinese surveillance ships and 10 fishing boats have anchored off the disputed Scarborough Shoal, with the fishermen taking giant clams and corals that are protected under Philippine law, a regional military spokesman said.

It is the largest number of Chinese vessels seen at the shoal since the two countries began a sovereignty standoff there almost a month ago, according to Major Loel Egos, whose northern command covers the area.

"They are just worsening the insult, bringing in all these fishing boats and all we can do is resort to diplomacy," Egos told AFP.

"They really want to test what a little country like the Philippines can do against a giant."

Egos said the Philippines, which has one of the weakest militaries in the region, has just two coast guard ships and a fisheries bureau vessel at the shoal that are unable to do anything about the Chinese fishing.

Asked about the increased Chinese presence, President Benigno Aquino's spokesman said the Philippines would show restraint.

"We do not wish to escalate any tensions right now," spokesman Edwin Lacierda told reporters.

"Therefore, what we're doing for now is to just to document the situation... and consequently, raise it before the (international) tribunals."

But foreign department spokesman Raul Hernandez called on China to "stop all forms of action that could aggravate the situation".

Ships from the two countries have been in a standoff over the shoal since April 8, after the Philippines detected eight Chinese fishing vessels there.

The Philippines sent its biggest warship to the shoal with the intention of arresting the fishermen, but two Chinese government vessels blocked those efforts.

The Philippines pulled back its warship shortly afterwards in an effort to lower the tensions and the initial batch of Chinese fishing vessels left, however both sides kept boats there to assert their sovereignty.

The Philippines says the shoal is well within the country's 200-nautical-mile exclusive economic zone, as recognised by international law.

But China claims the entire South China Sea as its historical territory, even up to the coasts of the Philippines and other Southeast Asian countries.