The Chinese air force has landed long-range bomber for the first time on an airport in the South China Sea.

It's a move likely to further fuel concerns in the region about Beijing's expansive claims over the disputed region.

The China Daily newspaper reported Saturday that People's Liberation Army Air Force conducted takeoff and landing training with the nuclear-capable H-6K bomber in the South China Sea.

A statement from the Defense Ministry late Friday says the exercise was conducted on an island reef at an unspecified "southern sea area."

An aerial view of construction at Mabini (Johnson) Reef by China, in the disputed Spratley Islands, in the south China Sea. ((Armed Forces of Philippines))

China has laid claim to a large portion of the South China Sea. (AAP) (AAP)

It involved several H-6Ks taking off from an air base then making a simulated strike against sea targets before landing.

"A division of the People’s Liberation Army Air Force (PLAAF) recently organised multiple bombers such as the H-6K to conduct take-off and landing training on islands and reefs in the South China Sea in order to improve our ability to 'reach all territory, conduct strikes at any time and strike in all directions'," the Defence Ministry said.

The US and others accuse Beijing of militarising the region to bolster its claims.

Last month China's military issued "robust" challenges to three Australian warships as they travelled through the South China Sea to Vietnam.

Defence sources say the confrontations between HMAS Anzac , HMAS Toowoomba and HMAS Success and the People's Liberation Army occurred before the Australian vessels' arrival for a three-day goodwill visit in Ho Chi Minh City.

China has been accused by regional neighbours of militarising seven reefs into island fortresses in a bid to dominate the disputed area of ocean.

A third of all global maritime traffic passes through the waterway and the area also has vast largely untapped oil reserves.