China's deployment of missiles to the disputed Spratly Islands shows Beijing is serious about exerting long-term domination and control over the South China Sea, and has no intention of keeping its promise not to militarise the contested area.

The placement of anti-ship missiles and surface-to-air missiles — if confirmed — will further ratchet up tensions over the South China Sea, particularly with those nations that have long laid claim to the Spratly Islands, including Taiwan and Vietnam.

For the first time, according to the US CNBC network, China has stationed missiles on three outposts in the Spratlys — Fiery Cross Reef, Subi Reef and Mischief Reef — which lie between Vietnam and the Philippines.

On one level the move is hardly surprising, given China has already placed missiles on Woody Island further north, and has installed military hardware on another artificial island in the Spratlys.

But this latest manoeuvre sends an implicit threat to other claimant nations that if they even try to exercise their rights to the Spratly Islands they will come within range of Chinese missiles.

China is capable of controlling the South China Sea militarily, according to US Admiral Philip Davidson. ( Reuters )

More importantly though, China's move represents a more explicit threat to the US, which has maintained an ongoing military presence in the South China Sea for decades, as a counter to Beijing's growing territorial ambitions.

The US is arguably the only nation with the power and motive to stop China's military expansion in the area.

After all the South China Sea is one of the busiest shopping lanes in the world.

Some estimates suggest as much as a third of all shipping passes through there.

But as Beijing continues to build its missile armoury and other military hardware in the South China Sea the chances of that happening steadily diminish — unless one or other side declares outright war.

The anti-ship missiles reportedly have the range and power to strike a vessel within about 300 nautical miles, and could easily destroy a US aircraft carrier.

Delicate balance for the Americans

China's missile deployment puts the US in an increasingly difficult position.

An international court ruling in The Hague in 2016 failed to contain China's territorial claims over the South China Sea. Diplomacy has had limited impact. But a military conflict remains unthinkable.

As US Admiral Philip Davidson said last month, "China is now capable of controlling the South China Sea in all scenarios short of war with the United States," and "would easily overwhelm the military forces of any other South China Sea claimants".

China's movement of missiles to Subi Reef, in the Spratly Islands, has angered other nations. ( Reuters: Francis Malasig )

The White House has warned there will be short and long-term consequences if China continues its militarisation of the South China Sea, in the wake of the CNBC reports.

But it gave no detail on what they might be. At least one defence analyst says China's military expansion spells all sorts of trouble for the US Navy.

"The biggest dilemma is that Beijing could, over time, deploy many more missiles than Washington's naval missile defence platforms could defend against," Harry Kazianis, the director of defence studies at the Center for the National Interest, told the CNBC network.

"At the end of the day, for Beijing, simple math means they would win a short-term military engagement."

In March, a US Navy ship angered China's military by sailing within 12 nautical miles of Mischief Reef, an artificial reef in the Spratlys that China seized from the Philippines in 1995.

The US regularly carries out Freedom of Navigation operations (FONOPs) in the South China Sea to reinforce its right to sail unimpeded through the area.

But Beijing called it a military provocation and ordered the ship to leave. Similarly, three Australian Navy ships were challenged by the Chinese military as they sailed through the South China Sea last month, towards Vietnam.

US and Australia forced to reconsider moves

Dr Euan Graham, the Director of International Security at the Lowy Institute in Sydney, says the latest manoeuvres in the Spratly Islands will force the US and allies, including Australia, to reconsider before sending ships into the South China Sea.

"The key point here is the US will still be able to operate. But it will have to adjust its procedures to pass through the Spratlys," he said.

"But for the South-East Asian countries and even smaller countries like Australia, France and the UK, which have been operating in the South China Sea recently, it'll be another ratcheting up of the threat level that will give politicians more pause for thought potentially before they commit to sending a single ship to prove a right to access."

At the same time, the threat is as much psychological as it is military.

"China's use of military power is a subtle one, in that it avoids fighting unless it absolutely has to," Mr Graham said.

"The key is not to do this in terms of military-on-military armed conflict. Rather it's how China uses this at a psychological level to shape and condition countries in the near region to a position of compliance. And they do that over time, both with a mixture of threats but also economic inducements. So it's a composite approach."