China accused the Philippines Thursday of not being sincere in seeking a peaceful end to a standoff over disputed waters, ramping up the rhetoric one day after confirming the deployment of more ships.

The Chinese foreign ministry made the remark as tension lingered over the Scarborough Shoal in the South China Sea, a vast body of water which stretches almost to the Equator and is claimed in its entirety by China.

"During the whole process, China has been appealing for diplomatic consultations to resolve the situation there," foreign ministry spokesman Hong Lei told a regular briefing.

"But the actions of the Philippine side cannot but raise our doubt over the sincerity of the Philippines to properly resolve the current situation."

As of early this week, there were five Chinese government vessels -- up from three -- and 16 fishing boats at the shoal, the Philippine foreign department said Wednesday.

Chinese state media later confirmed a "strengthened" presence, and Hong on Thursday also suggested that China had boosted the number of vessels.

"From the beginning of the incidents, China had launched solemn and immediate representations, demanding the Philippines to withdraw their vessels," he said.

"Now the Philippines is still taking some provocative actions there and China has to strengthen control and raise alert there."

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.

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

"We urge the Philippine side to respect China's territorial sovereignty in earnest and stop all provocations and show sincerity and carry out serious and earnest diplomatic dialogue with China," Hong said.

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.