The Philippines has called on China to withdraw more than 200 ships it accuses of encroaching upon its territorial waters in the South China Sea.
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?
Photos released by the Philippine coast guard show a row of Chinese ships moored at Whitsun Reef (called Julian Felipe Reef by the Philippines) in the South China Sea on 7 March.
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.
He accused the Chinese of a "provocative action of militarizing the area".
Chinese officials did not respond immediately when approached by foreign media for comment.
China plays down reports that it uses fishing fleets to help assert its territorial claims.
Two years ago, Philippine President Rodrigo Duterte defended his non-confrontational approach to the maritime dispute with a quip about Chinese President Xi Jinping.
"When Xi says 'I will fish' who can prevent him?" he said, quoted by the Associated Press. "If I send my marines to drive away the Chinese fishermen, I guarantee you not one of them will come home alive."