Chinese ships are still at the disputed shoal. Photo: Business Insider

The Philippines has accused China of aggressively colonizing the South China Sea, as fears of a major conflict between the two countries grow.

It comes as a U.S. carrier strike group, led by the USS Theodore Roosevelt, returned to the area for the second time in less than two months.

Hundreds of Chinese paramilitary ships are "swarming'' a South China Sea reef

Over the last couple of weeks, around 220 Chinese paramilitary ships, manned by maritime militias, have "swarmed" around a disputed reef in the South China Sea, with the Philippines warning that the "incursions" could "trigger unwanted hostilities" -- the toughest remarks yet from Manila.

China maintains that the vessels are simply fishing boats, sheltering in the area due to poor sea conditions -- but they have done no fishing and the weather has been good. They also switch on powerful lights at night. The Philippines' government says the vessels are part of China's maritime militia and manned by reservists operating under the orders of the Coast Guard and People's Liberation Army (PLA).

The boats are moored at the Whitsun Reef within Manila’s 200-mile exclusive economic zone, and there are fears the Chinese ships may try to claim the reefs. The Philippine defense minister has warned that Beijing is also planning to occupy and assert its control over more disputed territory, according to Fox News.

The reef is part of the Spratly Islands, one of the main disputed archipelagos in the South China Sea, some 200 miles west of the Philippine province of Palawan. The Philippines says the offshore region is part of its territory, but it is claimed entirely or in part by China, Brunei, Malaysia, Taiwan and Vietnam.

An international tribunal invalidated China’s claim to 90% of the South China Sea in 2016, but Beijing does not recognize the ruling. China has built islands in the disputed waters in recent years, putting airstrips on some of them. Taiwan, Malaysia, Vietnam, the Philippines and Brunei all claim parts of the sea.

US Theodore Roosevelt Carrier Strike Group Back in South China Sea

The aircraft carrier USS Theodore Roosevelt. Photo: NBC News

The U.S. 7th Fleet announced on April 6 that the Theodore Roosevelt Carrier Strike Group had entered the South China Sea two days before, on April 4, to conduct “routine operations.” This would be the second time this year that the strike group – consisting of flagship carrier USS Theodore Roosevelt, Carrier Air Wing 11, the Ticonderoga-class guided-missile cruiser USS Bunker Hill, Destroyer Squadron 23, and the Arleigh Burke-class guided-missile destroyer USS Russell – has entered that body of water as part of its tasking within the 7th Fleet’s area of operations, reported by The Diplomat.

According to the 7th Fleet statement, “While in the South China Sea, the strike group will conduct fixed and rotary-wing flight operations, maritime strike exercises, anti-submarine operations, coordinated tactical training, and more.”

The strike group had exercised with the Indian navy and air force in the Bay of Bengal at the end of March. According to a 7th Fleet statement on the occasion, the exercise focused on anti-submarine warfare, joint air operations, and command and control integration.

The Theodore Roosevelt’s return to the South China Sea comes amid growing regional tensions that – if left unchecked – threaten to boil over, as analysts continue to be apprehensive about China’s coercive posture toward Taiwan, and its use of maritime militia to enforce illegal claims in the South China Sea, most recently within the Philippines’ exclusive economic zone (EEZ).

According to a White House readout of a call between U.S. National Security Advisor Jake Sullivan and Philippine National Security Adviser Hermogenes Esperon on March 31, the two discussed the Whitsun Reef events, with Sullivan reaffirming “the applicability of the U.S.-Philippines Mutual Defense Treaty in the South China Sea.”