A Chinese research vessel was spotted off an island as the Philippines holds joint army exercises with its allies in the South China Sea.

The 'unauthorised' China-flagged ship was seen in the vicinity of Catanduanes province, around 60.9 nautical miles off Rapu-Rapu island, on April 25.

In a statement, the Armed Forces of the Philippines said: 'Per latest reports from Tactical Operations Wing, Southern Luzon (TOWSOL) who conducted maritime patrol (MARPAT) on April 27, it was observed that the vessel was lying-to in the area and had no personnel on the main deck.

'Several attempts to contact the vessel through regular radio channels were unsuccessful, indicating a lack of responsiveness or willingness to engage.

'The AFP remains vigilant, monitoring any unauthorized research vessel in our maritime domain. We have already tasked nearby vessels for enhanced surveillance and reporting.'

The sighting comes as the Philippines is conducting the 2024 Balikatan Exercises, which is said to be the biggest iteration yet involving some 16,700 soldiers from the country's allied nations.

It will run from April 22 to May 10, and will be carried out beyond the Philippines' 12-nautical-mile territorial zone.

However, China warned that the move will only worsen tensions in the disputed South China Sea.

Chinese foreign ministry spokesperson Lin Jian said: 'Attempts to bring in external forces to safeguard its so-called security will only lead to greater insecurity for itself.'

The Philippines has seen a number of clashes with Chinese vessels in the South China Sea in recent months.

Expansionist China currently lays claim over almost the entire South China Sea, one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.

The Communist rogue state - accused of genocide for its crimes against the Uyghur population - has been steadily increasing its influence in recent years through investment in developing countries.