Beijing irate as US vows to get tough on South China Sea

China has warned the US to ''speak and act cautiously'' after the White House said it would act to foil Chinese attempts to ''take over'' the South China Sea, amid growing hints that Donald Trump's administration intends to challenge Beijing over the strategic waterway.

At a press conference in Beijing today, foreign ministry spokesperson Hua Chunying urged Washington to tread carefully ''to avoid harming the peace and stability of the South China Sea''.

Hua was responding to comments made by White House press secretary Sean Spicer the previous day.

Speaking at a press briefing on Monday, Spicer vowed the US would ''make sure that we protect our interests'' in the route through which $4.5 trillion in trade passes each year. The sea is also rich in natural resources.

Spicer's comments came less than a fortnight after Exxon chairman Rex Tillerson, Trump's nominee for secretary of state, set the stage for a potentially explosive clash with Beijing by likening its artificial island building campaign in the South China Sea to ''Russia's taking of Crimea''.

Tillerson told his confirmation hearing the White House needed to send China a ''clear signal'' that such activities had to stop and that its access to such territories was ''not going to be allowed''.

''They are taking territory or control or declaring control of territories that are not rightfully China's,'' Tillerson said.

Chinese media responded by warning that any attempt to prevent China accessing its interests in the region risked sparking a ''large-scale war''.

At his first question and answer session with the press on Monday, Spicer again hinted Trump's administration would take a harder line on the South China Sea.

''It's a question of if those islands are in fact in international waters and not part of China proper, then yeah, we're going to make sure that we defend international territories from being taken over by one country,'' he told reporters.

Spicer declined to explain how such steps might be enforced. ''I think, as we develop further, we'll have more information on it,'' he said.

However, scholars who have been advising Trump's team on China policy back a more muscular military approach, primarily through a dramatically strengthened navy in the region.

''We've talked a big game on security but haven't really followed it up all that well with the military muscle that was needed,'' Daniel Blumenthal, the director of Asian Studies at the American Enterprise Institute, a conservative Washington-based thinktank, told the Guardian.

Blumenthal said a ''strong, persistent US naval presence'' was required to back up a foreign policy ''that at its bottom line says that China's not going to control the South China Sea … but you can't do that without military resources.''

China claims sovereignty over nearly the entire South China Sea and in recent years has stepped up a campaign to cement its control over a region where Brunei, Japan, Malaysia, the Philippines, Taiwan and Vietnam have claims.

It has done so partly by transforming a series of remote coral reefs into what experts say are effectively military outposts designed to help enforce its territorial claims.

Last month, a US thinktank said ''significant'' weapons systems, including anti-aircraft and anti-missile system, had been deployed on China's artificial islands. Beijing claims it has no intention of militarising the islands.

In July 2016, a judgment by an international tribunal in The Hague came down overwhelmingly in favour of claims by the Philippines to rocky outcrops in the South China Sea, a verdict disputed by Beijing.