The Philippines has protested the "illegal" presence of over a hundred Chinese boats around a disputed reef in the flashpoint South China Sea, describing it as a source of regional instability, the government said.
Authorities spotted the boats around the boomerang-shaped Whitsun Reef in April -- a year after a similar "swarming" incident caused a diplomatic row -- but the foreign office waited till Thursday to disclose it had launched a formal complaint with the Chinese embassy in Manila.
Manila and Beijing have long been locked in a dispute over parts of the South China Sea, almost all of which China insists it has exclusive rights to, rejecting a 2016 international tribunal ruling that its historical claims were without basis.
"The lingering unauthorised presence of Chinese fishing and maritime vessels is not only illegal, but is also a source of instability in the region," the Department of Foreign Affairs said.
"The Philippines calls on China to comply with its obligations under international law, cease and desist from displaying illegal and irresponsible behaviour, avoid further escalating tensions at sea and immediately withdraw all of its vessels from Philippine maritime zones."
The department did not disclose whether there had been a Chinese government response and whether the boats were still in the area.
China's embassy in Manila did not respond to requests for comment.
The foreign department said 210 Chinese vessels 'swarmed' around Whitsun from March 7 last year, lingering in the area for weeks.
Beijing said the vessels were fishing boats sheltering from bad weather, but Manila rejected the explanation, saying there was no storm in the area at the time.
Manila said it has filed more than 300 diplomatic protests over Chinese actions in the disputed waters over the past six years.
Last month, the foreign office said it had summoned a senior official of the Chinese embassy on April 13 to protest the harassment of a Taiwan marine research vessel with Filipino scientists on board by a Chinese coast guard ship.
It also filed a separate protest last month over China's annual practice of declaring a fishing ban over areas beyond its "legitimate maritime entitlements".
