China has deployed more government ships and fishing boats to a disputed shoal in the South China Sea amid a tense stand-off with Manila, the Philippine foreign department said Wednesday.

As of Monday night, there were five Chinese government vessels and 16 fishing boats in the area, along with 56 dinghies used by the fishermen to collect fish in shallow waters, Hernandez said.

Two Philippine government vessels monitoring Chinese activity previously reported only three Chinese government vessels near the Scarborough Shoal.

Manila had lodged a fresh protest with the Chinese embassy over the build-up near the shoal, department spokesman Raul Hernandez said.

"The Philippines, therefore, demands that China's vessels immediately pull out from Bajo de Masinloc and the Philippines' exclusive economic zone," Hernandez said, referring to the shoal's local name.

Chinese embassy officials were not immediately available to comment.

China claims the shoal along with most of the South China Sea, even up to the coasts of its Asian neighbours, while the Philippines says the shoal is well within its 200-nautical-mile exclusive economic zone.

Cranking up tensions, both countries have had ships posted around the shoal since early April, when Chinese vessels prevented a Philippine Navy ship from arresting Chinese fishermen.

The two claimants had vowed to de-escalate the tensions and both imposed separate fishing bans in the area from May 16, while Philippine President Aquino stopped a planned protest trip to the shoal by a Philippine ex-soldier.

Hernandez said that as of Tuesday, the number of Chinese dinghies around the shoal had risen to 76, while no Philippine fishing vessels were in the area.

"They are fishing and collecting corals," he said of the Chinese, apparently in violation of their government's own fishing ban.

He said the two governments were still in talks over the dispute, and the alleged Chinese build-up only served to "escalate tension" around the shoal.

Taiwan, Brunei, Vietnam and Malaysia also claim parts of the South China Sea.

The rival claims have for decades made the waters one of Asia's potential military flashpoints.