The Philippine Coast Guard reported that some 220 vessels, believed to be manned by Chinese maritime militia personnel, were seen moored in line formation at a reef on March 7, a cross-government task force said late on Saturday.

Foreign Minister Teodoro Locsin, asked whether he would file a diplomatic protest over the ships’ presence, told a journalist on Twitter: "Only if the generals tell me. In my watch foreign policy is the fist in the iron glove of the armed forces."

The National Task Force for the West Philippine Sea expressed concern about overfishing and destruction of the marine environment, as well as risks to safety of navigation.

An international tribunal in 2016 invalidated China’s claim to 90 percent of the South China Sea, but Beijing does not recognize the ruling. China in recent years has built islands in the disputed waters, putting air strips on some of them.

In January, the Philippines protested a new Chinese law allowing its coastguard to fire on foreign vessels, describing it as a "threat of war."

The United States has repeatedly denounced what it called China’s attempts to bully neighbors with competing interests, while Beijing has criticized Washington for what it calls interference in its internal affairs.

The Chinese vessels were at the Julian Felipe Reef, also called Whitsun Reef, in Manila’s exclusive economic zone, the task force said, describing the site as "a large boomerang-shaped shallow coral reef at the northeast of Pagkakaisa Banks and Reefs."

"Despite clear weather at the time, the Chinese vessels massed at the reef showed no actual fishing activities and had their full white lights turned on during night time," it said in a statement.

The Philippines vowed to monitor the situation and "to peacefully and proactively pursue its initiatives on environmental protection, food security and freedom of navigation" in the South China Sea.