The Sandy Cay reef lies near Thitu Island, or Pag-asa, where the Philippines stations troops and maintains a coast guard monitoring base.

Chinese state broadcaster CCTV said Saturday that the country's coast guard had "implemented maritime control" over Tiexian Reef, part of Sandy Cay, in mid-April.

The Philippines and China have been engaged in months of confrontations over the South China Sea, which Beijing claims nearly in its entirety despite an international ruling that its assertion has no legal basis.

"There is no truth whatsoever to the claim of the China Coast Guard that the (Sandy Cay sandbanks) have been seized," National Security Council spokesman Jonathan Malaya told a Monday press conference.

"It's in the interest of the People's Republic of China to use the information space to intimidate and harass," he said, calling the Sandy Cay report a "made-up" story that had been "irresponsible" to disseminate.

CCTV on Saturday published a photograph of four coast guard officials posing with a national flag on the reef's white surface, in what the broadcaster described as a "vow of sovereignty".

On Monday, the Philippine Coast Guard released its own photo showing Filipino sailors holding the country's flag over the same disputed reef during an early morning mission the day before.

There do not appear to be any signs that China has permanently occupied or built a structure on the reef, which is a group of small sandbanks in the Spratly Islands.

In recent months, Beijing and Manila have blamed each other for causing what they describe as the ecological degradation of several disputed landforms in the South China Sea.

The US and Philippine militaries are currently conducting joint exercises that Beijing has said constitute a threat to regional stability.

Chinese warships have been spotted in Philippine waters since those bilateral "Balikatan" exercises kicked off last week, with aircraft carrier Shandong reportedly coming within 2.23 nautical miles (about four kilometres) of northern Babuyan Island.