BEIJING (REUTERS) - China has drilled deep in the South China Sea to retrieve sediment core from the seabed, state media reported on Thursday (April 8), amid tensions over disputed waters with rival claimants Taiwan and the Philippines, as well as with the United States.

Chinese scientists on a marine research vessel used China's home-made Sea Bull II drilling system to obtain a sediment core 231m long at a depth of 2,060m, the official Xinhua news agency said.

The system can help explore natural gas hydrate resources in the seabed, Xinhua added, referring to the solid ice-like crystals formed from a mixture of methane and water that are touted as a promising source of energy.

It was unclear exactly where the drilling took place in the South China Sea, around 90 per cent of which is claimed by Beijing as its territorial waters. Malaysia, the Philippines, Taiwan, Vietnam and Brunei also lay claim to parts of the sea, which has vast oil and gas potential.

Tensions in the region have escalated since a US Navy strike group entered the South China Sea on Sunday. That came after the president of the Philippines, a US ally, voiced concern about Chinese vessels massing in Manila's 320km exclusive economic zone.

Taiwan - which China sees as a breakaway province to be reunited with the mainland, by force if necessary - has threatened to shoot down Chinese drones spotted circling the Taipei-controlled Pratas Islands in the South China Sea.

China's oil and gas exploration activities in the South China Sea have stoked tensions before, notably when state-run China National Offshore Oil Corp deployed a deepwater drilling rig in Vietnam-claimed waters in 2014.