China used a high-decibel sonic device to allegedly harass a Philippine Coast Guard (PCG) vessel off the coast of the Philippines.

Footage shows the Communist-controlled Coast Guard vessel CCG 3103 blasting the loud siren while sailing near the PCG's BRP Cabra ship around 95 nautical miles from the shore of Zambales province, on January 25.

PCG crew said the 'defeaning' noise came from a Long Range Acoustic Device employed by the CCG to deter proximity.

PCG spokesman Commodore Jay Tarriela said: 'This is our first time to experience the China Coast Guard's long-range acoustic device, which our personnel said hurt their ears. It was in very close proximity to our ship. The Chinese ship had difficulty moving forward because the BRP Cabra was just a few hundred yards away from them.'

Despite the alleged harassment, the PCG said the aggressive Chinese ship was 'successfully' prevented from approaching the Philippine coastline.

Defense analyst Dr. Renato de Castro said China was employing 'gray zone operations' to assert Beijing's territorial claims over the disputed waters.

He said: 'They are using coercive actions, harassment, and other measures short of the actual use of force. Although there is no kinetic or lethal use of force, this is an indication that their actions are hostile and troubling. The intrusive patrols they are conducting are also done against other Southeast Asian countries like Malaysia.'

The Chinese vessel is just one of several sent near the coast of the Philippines on maritime patrol.

Among them is the massive CCG 5901, the world's largest coast guard vessel at 541 feet and 12,000 tons, which started lurking off the seaside province of Zambales on January 4 afternoon.

Authorities believe the ships were deployed to intimidate Filipino fishermen from entering the Scarborough Shoal, a disputed fishing ground and resource-rich area in the South China Sea.

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 Communist rogue 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.