China has accused the Philippines of repeated encroachment in its waters. China with its largest navy in the world claims most of the South China Sea, a key conduit for $3 trillion of annual ship-borne trade, as its own territory, with a massive coast guard presence in and around the EEZs of neighbours Vietnam, the Philippines, and Malaysia.

Observers interpret the presence of the 165-metre vessel near Scarborough Shoal as a warning to Manila about its military ties with the US.

The Philippines has accused a giant Chinese coast guard vessel it dubbed as the “Monster” of maintaining an “illegal presence” in its exclusive economic zone as Beijing ramps up activities in the disputed South China Sea.

The Philippines has deployed air and sea assets of its military and coast guard in its exclusive economic zone to monitor China's largest coast guard vessel, calling the ship's presence an act of Chinese "intimidation,

Malacaang expresses "grave concern" over the presence of China's so-called monster ship off the coast of Zambales, adding that the Philippines is actively challenging its presence.

The Armed Forces of the Philippines (AFP) stressed Tuesday that it will not be deterred in performing its mandate of patrolling our seas and air despite the presence of China Coast Guard (CCG) vessel 5901 within the country’s exclusive economic zone (EEZ).