Vibrant reefs filled with colorful fish and seaweed just two years ago have been turned into a wasteland of crushed corals in the South China Sea and the Philippines says it has identified a culprit -- China's shadowy maritime militia.

China has rejected the accusation, setting up another public disagreement with its neighbor over the flashpoint waterway.

Videos released Monday by the Philippine Coast Guard showed a vast patch of bleached corals along the Rozul (Iroquios) Reef and Sabina (Escoda) Shoal in the South China Sea, which are underwater features within the country's internationally recognized exclusive economic zone (EEZ).

Both reefs are near Palawan, the Philippines' southwestern island chain fronting the South China Sea, but Beijing claims most of the large and strategic waterway as its own territory despite competing claims by neighbors and in defiance of an international ruling.

Commodore Jay Tarriela, the coast guard spokesman, said divers had carried out "underwater surveys" of the seabed and described "visible discoloration" that indicated "deliberate activities" meant to modify the natural topography of the terrain.

"The continued swarming for the indiscriminate illegal and destructive fishing activities of the Chinese Maritime Militia in Rozul Reef and Escoda Shoal may have directly caused the degradation and destruction of the marine environment in the [West Philippine Sea] features," Tarriela said in a statement, referring to Manila's name for parts of the South China Sea within its jurisdiction.

Tarriela said between August 9 and September 11, the coast guard monitored 33 Chinese vessels within the vicinity of Rozul Reef and around 15 Chinese ships near Escoda Shoal.

"The presence of crushed corals strongly suggests a potential act of dumping, possibly involving the same dead corals that were previously processed and cleaned before being returned to the seabed," Tarriela added.

The Philippine military last Saturday also accused China's maritime militia of massive destruction in the area.

Chinese authorities did not comment publicly on the accusations until Thursday when the foreign ministry was asked at a regular daily briefing about the destruction of the corals.

"The relevant allegations of the Philippine side are false and groundless," spokesperson Mao Ning told reporters. "We advise the Philippine authorities not to utilize fabricated information to stage a political farce."

Beijing claims "indisputable sovereignty" over almost all of the 1.3 million square miles of the South China Sea, as well as most of the islands and sandbars within it, including many features that are hundreds of miles away from China's mainland. That includes the Spratlys, an archipelago consisting of 100 small islands and reefs also claimed in full or part by the Philippines, Malaysia, Brunei and Taiwan.

Over the last two decades China has occupied a number of reefs and atolls across the South China Sea, building up military installations, including runways and ports, which have not only challenged the Philippines' sovereignty and fishing rights but also endanger the marine biodiversity in the highly contested resource-rich waterway.

Some of the atolls and islands that were built on saw sustained land reclamation take place, often with reefs being destroyed first and then built on.

In 2016, an international tribunal in The Hague ruled in favor of the Philippines in a landmark maritime dispute, which concluded that China has no legal basis to claim historic rights to the bulk of the South China Sea.

But Beijing has ignored the decision and continues to expand its presence in the waterway.

'A wake-up call'

The recent Philippine coastguard footage of broken and bleached coral is in stark contrast to just two years ago.

The University of the Philippines Marine Science Institute said in a statement to CNN it had surveyed a portion of the Rozul (Iroquios) Reef in 2021 through an expedition funded by the country's National Security Council on board M/Y Panata.

Videos and photos taken by the institute in 2021 showed the Rozul (Iroquios) Reef specked with red and purple colored corals with aquatic algae and moss lining the reef.

"At that time, we found that the surveyed area had a reef ecosystem, with corals, benthic animals, fishes, seaweeds, and other marine organisms," it said, but stopped short on commenting on the current status of the reef since the latest information from the Philippine army and coast guard were "beyond the purview" of the institute.

"That said, we are open to working with other agencies to validate and analyze the impacts of recent activities in the area. Situations like this emphasize the need for continuous monitoring and support for more Marine Scientific Research activities by Filipino scientists especially in the West Philippine Sea," it added.

Signs of the marine degradation underscored the threats of coral harvesting in the territory, prompting several Filipino senators to raise suspicion over whether China has plans to militarize the atolls through reclamation, CNN affiliate CNN Philippines reported.

"It's a wake-up call," said Gerry Arances, executive director of the Center for Energy, Ecology and Development (CEED).

The images have exposed the marine impacts of China's construction of island facilities in the waters, frequent militia vessel patrols and expansive commercial fishing, Arances said.

"It surfaces a lot of weaknesses, in terms of monitoring, regulating, and overall protecting marine biodiversity," he said.

Western marine security experts, along with officials from the Philippines and the United States, have increasingly accused Beijing of using ostensibly civilian fishing vessels as a maritime militia that acts as an unofficial -- and officially deniable -- force that China uses to push its territorial claims both in the South China Sea and beyond.

Dubbed Beijing's "little blue men", Chinese fishing vessels have also been involved in clashes with fishing vessels from Indonesia and Vietnam in contested waters.

Last month, the Philippines said a clash between Chinese coastguard and Philippine vessels included at least two blue-hulled vessels that looked like fishing vessels.

"There has been a collective failure internationally to respond to China's actions in the South China Sea, with regard to its militarizing the reefs and the shoals where China has, over a period of time, taken pristine marine features and turned them into concrete military bases and the collective response of much of the environmental advocacy groups has been silenced," said Ray Powell, director of SeaLight at the Gordian Knot Center for National Security Innovation at Stanford University.

The Philippines' growing calls for transparency on China's maneuvers in the disputed waters have enabled the country to garner international support from its allies to affirm its territorial sovereignty, Powell added.

At least two foreign ambassadors in Manila have expressed alarm over reports of destruction of marine resources in the South China Sea.

United States Ambassador to the Philippines MaryKay Carlson described the reports on coral destruction around the reefs as "troubling," according to a post on X, formerly known as Twitter.

"Habitat damage harms ecosystems and negatively affects lives and livelihoods. We are working with our #FriendsPartnersAllies to protect [the Philippines'] natural resources," she said on Monday.

Japanese Ambassador Kazuhiko Koshikawa also described the development as "very alarming news," as he urged everyone to protect "these vital ecosystems."

The Philippine Department of Foreign Affairs said in a statement that the country has "consistently raised the alarm over ecologically harmful activities, conducted by foreign vessels" in its maritime zones.

Former president Rodrigo Duterte had attempted to forge closer ties with Beijing and made plans to cooperate on oil and gas exploration in the South China Sea, a move which divided Filipinos over the legitimacy of enabling China's ambitions in the disputed territory.

According to the Asia Maritime Transparency Initiative, the Philippines occupies nine features in the Spratly chain while China occupies seven. But Beijing, which calls the island chain the Nansha Islands, has built up and fortified much of its claims in the chain, including building military bases on places like Subi Reef, Johnson Reef, Mischief Reef and Fiery Cross Reef.

By contrast, only one of the Philippine-controlled features even has a runway, namely Thitu Reef.

In 1999, the Philippines intentionally grounded a navy transport ship, the BRP Sierra Madre, on Second Thomas Shoal, manned by Filipino marines, to enforce the country's claim to the area.

At Thursday's press briefing, Chinese foreign ministry spokesperson also referenced the Sierra Madre.

"If the Philippine side is really concerned about the ecological environment of the South China Sea, it should tow away the warships illegally sitting on the Ren'ai Reef as soon as possible and stop discharging sewage into the sea, and also to prevent irreversible damage to the sea caused by the warships that continue to rust," she said, using the Chinese name for the reef.

Under current President Ferdinand Marcos Jr., the country's National Security Team began to publicize its findings about what was actually happening in the West Philippine Sea and the South China Sea more regularly, Powell said.

"The Philippine government's transparency policy really earned it a lot of domestic support to push back and international support for its position," he said.