The vessels were first spotted on Thursday, a day after a YouTube video appeared in which Philippine President Ferdinand Marcos said there was no way Manila could stay out of conflict if China invaded Taiwan.
China considers self-ruled Taiwan to be part of its territory and has threatened to seize it by force.
The three Chinese vessels were spotted near Batanes province, a remote group of sparsely populated islets north of the Philippines' largest island, Luzon.
An aircraft was deployed on Friday to monitor the "irregular movements" of the three Chinese ships near the Batanes islands, the Philippine Coast Guard said in a statement.
China Coast Guard ship 4304 was located about 140 kilometres (85 miles) west of Sabtang town but bad weather prevented authorities from getting close to the locations of the other two vessels, it said.
Marcos said in an interview with Indian news agency Firstpost that, in the event of a confrontation between China and the United States over Taiwan, "there is no way that the Philippines can stay out of it simply because of our physical geographic location".
"If there is an all-out war, then we will be drawn into it," he said in the interview, which was uploaded on YouTube on Wednesday.
He also said many Filipinos living in Taiwan would need to be rescued and repatriated.
China has lodged a protest with the Philippines over Marcos's remarks.
"We urge the Philippines to earnestly abide by the one-China principle... and refrain from playing (with) fire on issues concerning China's core interests," a foreign ministry spokesperson said on Friday.
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