Beijing’s People’s Liberation Army (PLA) used Harbin Z-9 helicopters during the drill, which then fired live missiles at simulated targets. According to the United States Naval Institute (USNI), the missiles, launched “several days ago”, were “anti-ship” variants.

The helicopters reportedly took off from a base at Sanya – the southernmost city on China’s Hainan Island.

The USNI said the base is “crucial”, stating it had the ability to “make a difference in the balance of power in the region”.

Chinese forces appear to be improving the base, with satellite images allegedly revealing the construction of a new dry dock.

US analysts said the base has been in the works for around four years, and its size suggests it will be capable of accommodating China’s upcoming Type-003 supercarrier ship.

The aircraft carrier is currently being built in Shanghai, and is estimated to be larger in size than China’s previous two carriers which were based on old Russian designs.

The upcoming ship is also expected to make use of an electromagnetic catapult used to launch aircraft, similar to US aircraft carriers.

READ: South China Sea fury: Beijing military bases ‘vulnerable to attack’ amid growing tensions

The South China Sea is a source of tension between the US and China.

US Secretary of State Mike Pompeo said earlier this year: “We are making clear: Beijing’s claims to offshore resources across most of the South China Sea are completely unlawful, as is its campaign of bullying to control them.

“We stand with the international community in defence of freedom of the seas and respect for sovereignty and reject any push to impose ‘might makes right’ in the South China Sea or the wider region.”

Zhao Lijian, China’s Foreign Ministry Spokesperson, hit back, saying: “China’s territorial sovereignty and maritime rights and interests in the South China Sea are solidly grounded in history and law and consistent with relevant international law and practice.

“The US, as a country outside the region, wishes nothing but chaos in the South China Sea so that it can gain from the muddied waters.”

More recently, US naval forces also conducted a Freedom of Navigation exercise in South China Sea waters claimed by Vietnam.

On Christmas Eve, the USS John S McCain “asserted navigational rights” in the vicinity of the Con Dao Islands.

The US Navy’s 7th Fleet said in a statement: “The ship conducted normal operations within Vietnam’s claimed territorial seas to challenge excessive maritime claims and preserve access and navigational freedoms consistent with international law.”