The Philippine coast guard is conducting drills in the South China Sea which an official said Sunday were part of efforts to secure "our maritime jurisdiction" over the disputed waters.

The exercises near the Philippine-occupied Thitu Island and China-controlled Scarborough Shoal come amid heightened tensions over the resource-rich sea.

The latest diplomatic wrangle between the two countries was triggered by the detection last month of hundreds of Chinese vessels in the Spratly Islands.

Most of the boats have since dispersed around the contested archipelago.

China -- which claims almost the entirety of the sea -- has refused repeated demands by the Philippines to call back the ships, which Manila says are maritime militia vessels and Beijing says are fishing boats.

In response, the Philippines has deployed more patrol vessels, including coast guard and navy ships, to intensify surveillance and prevent illegal fishing.

The coast guard drills began last week.

"We are supporting the whole-of-nation approach in securing our maritime jurisdiction," coast guard spokesman Commodore Armando Balilo said.

A Philippine coast guard ship sails past a Chinese coast guard ship near Scarborough shoal in the South China Sea in May 2019
A file picture of a Philippine coast guard ship sailing past a Chinese coast guard ship near Scarborough shoal in the South China Sea AFP / TED ALJIBE

The exercises involve training in navigation, small boat operations, maintenance and logistical operations.

They are being held near Thitu Island and Scarborough Shoal, as well as the Batanes islands in the north, and the southern and eastern parts of the country.

Scarborough -- one of the region's richest fishing grounds -- has long been a flashpoint between Manila and Beijing.

China seized it from the Philippines in 2012 following a tense standoff.

The drills began as Philippine armed forces held joint exercises with US soldiers that ended Friday.

Beijing has ignored a 2016 international tribunal decision that declared its historical claim over most of the South China Sea to be without basis.

But once-frosty relations between Manila and Beijing have warmed under President Rodrigo Duterte, who set aside the ruling in exchange for promises of trade and investment.

The Philippine foreign and defence secretaries, however, have been engaged in a war of words with Beijing.

The foreign affairs department has been filing daily protests over the Chinese vessels and, in a rare move, recently summoned Beijing's envoy to express its "utmost displeasure" over the issue.