China's expanding military presence in the region has worried several of its neighbours, while the US has vowed to stand up against Beijing's territorial claims to much of the South China Sea, including the contested Paracel Islands.

Chinese H-6G and H-6J jet bombers carried out "high-intensity training, and completed day-and-night training exercises in taking off and landing, long-range assault, and attacks on sea targets," defence ministry spokesman Ren Guoqiang said at a virtual press conference Thursday.

Ren said the exercises were part of routine training and had "achieved the expected results", without giving their specific location.

China -- which is locked in disputes with neighbours including India, Japan and Vietnam over islands in the South China Sea -- has infuriated other nations by building artificial islands with military installations in parts of the sea.

Washington declared earlier this month that Beijing's claims to most of the sea are illegal, ramping up support for Southeast Asian nations with claims to parts of it.

The region is believed to have valuable oil and gas deposits.

Australia has also rejected Beijing's territorial and maritime claims in the sea, saying there was "no legal basis" to several of China's claims.

The US regularly conducts so-called "freedom of navigation operations" in the South China Sea in order to stand up to Beijing, with the US Navy sometimes sending warships to the Paracels.