If Donald Trump's hawkish new administration follows through on threats and tries to cut Beijing off from artificial islands in the South China Sea, it could face a stiffer pushback than many imagine, experts say.

The US president and his team have made much of their desire to put Beijing in its place, including in the strategically vital waterway, which China claims almost entirely and where it has reclaimed -- and fortified -- thousands of acres of land, according to the Pentagon.

Trump's nominee for Secretary of State, Rex Tillerson, told his confirmation hearing the US needs to send a clear signal that China's access to the islands is "not going to be allowed".

Observers quickly pointed out the full-scale blockade this would require was likely to provoke a military response from Beijing -- a response that might be enough to make the US think twice.

While Beijing may have a poorer and less well-equipped military, it is stocking its arsenal with submarines, anti-ship missiles and other weapons tailor-made to neutralise Washington's most valuable naval assets, they say.

"Beijing knows that it cannot win a conventional frontal conflict with the US," with its vastly superior military, Valerie Niquet of French think tank Foundation of Strategic Research told AFP.

Instead, it is developing "capacities that would restore its freedom to manoeuvre by pushing Washington to hesitate before a potentially costly intervention in Asia."

- Flexing muscles -

China's island building programme in the South China Sea has irked neighbours -- many of whom also have claims to parts of the sea -- and caused global concern.

Beijing has ignored international condemnation over its construction of airstrips and installation of anti-aircraft batteries on one-time reefs.

It has dismissed an international arbitration court that ruled last year there was no basis for its claims over the South China Sea.

Former US President Barack Obama occasionally sent warships and planes through the area in so-called "freedom of navigation" exercises, but critics say he did not do enough to prevent China gaining a substantial foothold.

Trump, who threaded anti-China rhetoric throughout his election campaign, has indicated he is going to be a lot firmer.

"If those islands are, in fact, in international waters and not part of China proper, yeah, we'll make sure we defend international interests from being taken over by one country," new White House press secretary Sean Spicer said Monday.

Beijing is flexing its military muscle in response to the warnings.

Three days after Trump's inauguration, China's navy announced the delivery of the CNS Xining destroyer, nicknamed the "carrier killer" for its large load of anti-ship and land attack cruise missiles.

Beijing also possesses DF-21 and DF-26 anti-ship missiles that could secure it "a credible denial of access" against the US Navy, a source with knowledge of Chinese military activities told AFP.

While the US has around a dozen aircraft carriers, Beijing has just one: the second-hand, Soviet-built Liaoning. A second is under construction.

The Liaoning conducted its first live fire drill in December before heading to the South China Sea.

China's naval capacities "might not be enough to decisively destroy hostile modern navies, yet they are enough to deny or impede their access to some extent," Noboru Yamaguchi of the International University of Japan told AFP.

- 'Bring China more respect' -

While China has made significant progress in developing its military over the past two decades, it remains far behind the US, whose military budget is three times higher, at nearly $600 billion.

"Most analysts agree that it is 20 or 30 years behind the US in terms of military capabilities," said James Char of Singapore's Nanyang Technological University.

A major Achilles heel for the People's Liberation Army (PLA) is that it has not fought a real battle since a war with Vietnam in 1979, and has a questionable mastery of modern military techniques, according to some Western experts.

And while the West has NATO as a channel through which to share military experiences, China has no similar outlet, despite periodic joint exercises with other countries such as Russia.

As Niquet sees it, "Beijing must play a delicate balancing game so as not to go too far in their threats and provoke an American intervention" with unthinkable consequences.

So far, China is playing it cool in the face of Washington's rhetoric, with the foreign ministry largely avoiding any statements that might raise the temperature.

But "there certainly exists the worst-case probability of a destructive showdown" over access to China's artificial islands an editorial in the state-run China Daily warned Wednesday.

And "if there is to be 'war' in the South China Sea it will be because of actions by the US military."