Chinese militia vessels were seen allegedly swarming a contested reef in the South China Sea.

Aerial footage shows the Chinese boats lurking at the Rozul Reef, a disputed maritime feature near the resource-rich Spratly islands, on June 19.

The Philippine Coast Guard (PCG) said the fleet of more than 50 fishing vessels, used by Beijing as an auxiliary military force, were spotted some 130 nautical miles off Palawan in the Philippines.

In a statement, PCG spokesman Commodore Jay Tarriela said the PCG deployed two ships and an aircraft to investigate the situation.

He said: 'The PCG vessels and aircraft promptly challenged these vessels via radio, notifying them that they were operating within the Philippines' Exclusive Economic Zone (EEZ), approximately 130 nautical miles off the coast of Palawan. The PCG emphasized that the irregular patterns of movement, along with their anchoring and swarming activities, violate the principles of freedom of navigation and infringe upon the sovereign rights of the Philippines in its EEZ.

'The Chinese Maritime Militia vessels were directed to clarify their intentions, cease their swarming behaviors, and navigate in accordance with the Philippine Maritime Zones Act, the United Nations Convention on the Law of the Sea (UNCLOS), and the 2016 Arbitral Award. Unfortunately, no response was received from the CMM vessels.'

Expansionist China currently lays claim over almost the entire South China Sea, one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.

The rogue communist state - accused of genocide for its crimes against the Uyghur population - has been steadily increasing its influence in recent years through investment in developing countries.