The Philippines says over 100 Chinese vessels have dropped anchor inside the country's exclusive economic zone in the South China Sea.
The Philippines' foreign ministry said in a statement on Thursday the ships appeared in early April about 300 kilometers west of Palawan Island.
Photos released by the ministry show large vessels moored in lines and fitted with what look like cranes.
Officials say 55 ships were still in the area as of the end of May.
The statement says their presence is "not only illegal, but is also a source of instability in the region." The ministry called on China to immediately remove the ships from Philippine waters.
The Philippine government summoned the Chinese ambassador about a year ago, when over 200 Chinese vessels were spotted in the same area.
The latest move comes three weeks before the new Philippine president takes office.
Ferdinand Marcos Jr. has said he will push for talks with Beijing over their territorial disputes in the South China Sea. He says he will invoke a 2016 arbitration tribunal ruling that dismissed most of China's claims in the waters.