China’s claim to have seized a tiny sandbank in the South China Sea fits into Beijing’s “established pattern of illegal pressure” in the region, according to an expert. State media in China released images of four coast guard officers waving the Chinese flag on a disputed reef as part of an escalating regional dispute with the Philippines.

Professor Justin Bronk, from the defence think tank RUSI, said the move is part of plans by China to expand its footprint in the contested region. “While these bits of land are often incredibly small, they are used to claim or reinforce significant territorial claims around them,” the expert told the Express. China has a very long history of dredging and building reefs, essentially to create artificial islands which are big enough to house airbases and defensive or offensive weapons systems, essentially creating new land to make it easier for them to enforce claims across the whole of the South China Sea.

“It fits within an established pattern of illegal pressure. But the Chinese line is to insist that everything inside the Nine-dash line is Chinese domestic business, which nobody else recognises.”

Both China and the Philippines stake claims on various islands in the South China Sea which is a vital trade route for global supply chains.

China claims almost all of it, but these are not supported by international law and are disputed by other nations, including the Philippines.

Chinese state broadcaster CCTV said Beijing had "implemented maritime control and exercised sovereign jurisdiction" on the 200 sq metre Sandy Cay in the Spratly Islands earlier this month.

The Philippines responded by releasing an image, said to be taken at Sandy Cay, of officers holding up their national flag, mimicking the Chinese photo.

Manila’s National Task Force West Philippine Sea said it witnessed "the illegal presence" of a Chinese Coast Guard vessel 1,000 yards (914 metres) from one of the sandbanks.

"This operation reflects the unwavering dedication and commitment of the Philippine Government to uphold the country's sovereignty, sovereign rights and jurisdiction in the West Philippine Sea,” the statement said.

China’s coast guard described the Philippine landing as “illegal” and said that Chinese officers had gone ashore “to conduct on-site verification and enforcement measures”.

The assistant director general of the Philippine National Security Council said on Monday there is no truth to claims that China has seized the sandbars.

The White House earlier said that the reports of China seizing the reef were “deeply concerning if true”.

Sandy Cay is near a Philippine military outpost on Thitu Island and Subi Reef, which China has transformed into a base with a military-grade runway and buildings with communications facilities.

The dispute over Sandy Cay came days after the US and the Philippines launched their large-scale annual joint military drills.