Several bombers of various types -- including the long-range, nuclear strike capable H-6K -- carried out landing and take off drills at an unidentified island airfield after carrying out simulated strike training on targets at sea, the Chinese airforce said in a statement Friday.

Wang Mingliang, a defense expert cited in the statement, said the takeoff and landing exercises on islands in the South China Sea will help the air force "strengthen its combat capability to deal with martime security threats".

The move comes weeks after US network CNBC reported that China had installed anti-ship and air-to-air defences on outposts in the Spratly Islands that are also claimed by Vietnam and the Philippines, citing sources close to US intelligence.

Washington warned that Beijing would face unspecified "consequences" over its militarisation of the South China Sea, and said it had raised the issue with China.

"I believe this is the first time a bomber has landed in the #SouthChinaSea," Bonnieh Glaser, a China expert at the Centre for Strategic and International Studies, tweeted.

In an analysis published on its website, CSIS said the location of the runway was believed to be Woody Island, China's largest base in the Paracel Islands, which is also claimed by Vietnam and Taiwan.

The South China Sea issue has been brewing for years, with China, the Philippines, Brunei, Malaysia and Vietnam making competing claims in waters with vital global shipping routes and what are believed to be significant oil and natural gas deposits.

China has engaged in years of land-reclamation efforts on reefs it controls in the region and built both civilian and military facilities in the contested area.

Chinese military facilities include air bases, radar and communications systems, naval facilities and defensive weaponry including landing strips able to accommodate military planes.