"China, my friend, how politely can I put it? Let me see... O... GET THE FUCK OUT," Foreign Secretary Teodoro Locsin tweeted.

The latest spat between Manila and Beijing over the resource-rich waters -- which China claims almost entirely -- flared up in March after hundreds of Chinese boats were spotted inside the Philippines' Exclusive Economic Zone.

China has refused repeated calls from the Philippines to withdraw the boats, and tensions have intensified as Manila steps up maritime patrols in the area.

Locsin frequently uses strong language on Twitter and defended his latest outburst by saying: "Usual suave diplomatic speak gets nothing done."

He also likened China to "an ugly oaf forcing your attentions on a handsome guy who wants to be a friend".

The order came as his foreign affairs department accused China's coastguard of "belligerent actions" against Filipino boats involved in maritime drills near the contested Scarborough Shoal.

China-controlled Scarborough is one of the region's richest fishing grounds and a flashpoint between the two countries, which have rival claims.

The department said it has lodged a diplomatic protest over the Chinese vessels' actions towards the Southeast Asian country's coastguard during patrols and training exercises near the reef last month.

The department said the presence of the Chinese boats was a "blatant infringement of Philippine sovereignty".

China's embassy in Manila did not immediately respond to a request for comment.

Scarborough Shoal is 240 kilometres (150 miles) west of the Philippines' main island of Luzon.

China seized it in 2012 and has subsequently ignored a 2016 international tribunal decision that declared its historical claim over most of the South China Sea to be without basis.

Once-frosty ties between the two countries had warmed under President Rodrigo Duterte, who set aside the ruling in exchange for promises of trade and investment that critics say have largely not materialised.

Facing growing domestic pressure to take a harder line, Duterte said last week the Philippine maritime patrols would continue, insisting its sovereignty over the waters was not negotiable.