Beijing claims most of the South China Sea despite an international ruling that its assertion has no legal basis.

The Philippines said China's deployment this month of a "monster" coast guard vessel demonstrated Beijing's "increasing aggression" in the disputed waterway.

"It's getting closer to the Philippine coastline... and that is alarming," National Security Council spokesman Jonathan Malaya told journalists Tuesday.

Chinese ships have been deployed closer to the Philippine coast this year, Malaya said, with the latest movements an "intimidation tactic" intended to discourage Filipino fishing.

"We do not and will not dignify these scare tactics by backing down. We do not waver, or cower in the face of intimidation," said Malaya,

The 165-metre (540-foot) "monster ship" was last located 143 kilometres (89 miles) west of Capones Island in Zambales province.

Jay Tarriela, a Philippine Coast Guard spokesman, said "it doesn't really carry out very aggressive action, but its mere presence is already concerning".

The Philippine Coast Guard has deployed 84-metre and 97-metre vessels to pressure the Chinese ship "to move further away from the coast of Zambales," Tarriela said.