Defence Minister Delfin Lorenzana said the Chinese ships were violating the Philippines' maritime rights.

The Philippines says the fishing boats do not appear to be fishing and are crewed by China's maritime militia.

Five years ago an international court rejected Chinese claims of sovereignty over 90% of the water mass.

The Philippines, Brunei, Malaysia, Taiwan and Vietnam have all been contesting China's claim to almost all of the Sea for decades but tension steadily increased in recent years.

Beijing continues to claim an area known as the "nine-dash line" and has backed its claim with island-building and patrols, expanding its military presence while maintaining that its intentions are peaceful.

What is the Philippine position?

The reef lies within the Philippines' exclusive economic zone, the country's cross-government task force said on Saturday.

According to the Philippines, China had about 220 vessels moored at the reef.

"We call on the Chinese to stop this incursion and immediately recall these boats violating our maritime rights and encroaching into our sovereign territory," Defence Minister Lorenzana said.

Photos : satellite images by Maxar technologies, Tuesday, March 23 . Fishing vessels spotted on the Whitsun Reef called Julian Felipe Reef by the Philippines. 

Source : Site BBC