CCG 5901 had already left the coastline off the Philippine province of Zambales, the Philippine Coast Guard said.

The PCG has been monitoring the "monster ship" since last Saturday, when it was spotted by the Dark Vessel Detection system 54 nautical miles off Capones Island in Zambales.

China's largest Coast Guard vessel has begun to sail away from the waters off Zambales after loitering there for four days, only to be replaced by another Chinese ship in what authorities call a calculated move to maintain Beijing's illegal presence in the area.

China’s “monster ship” continues to operate near Luzon for the fourth consecutive day, the Philippine Coast Guard reported Tuesday night.

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

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

A Chinese navy helicopter hovered over a Philippine Coast Guard (PCG) vessel as China's monster ship lingered in Philippine waters. Footage shows the People's Liberation Army-Navy (PLA-N) aircraft with tail number 47 circling above the PCG BRP Cabra monitoring the gargantuan China Coast Guard (CCG) vessel 5901 some 70 nautical miles off Zambales province on January 7.