The US has deployed an aircraft carrier strike group to patrol the South China Sea, days after Beijing told Washington not to challenge its supposed ownership of the waterway.

China says the sea, which is resource-rich and a $5 trillion shipping lane for Asia, is almost entirely under its control, and has been militarizing islands there in an effort to bolster its claim over a host of other countries.

Trump is now continuing Obama's practice of sending US carriers through to assert that the sea is international waters, and has sent in the USS Carl Vinison.

But threats of military action from Chinese state media, Rex Tillerson's recent hint at a blockade, and recently emerged recordings of Steve Bannon, Trump's closest aide, predicting a Chinese was in 'ten years' mean the situation now is hotter than ever.

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The USS Carl Vinison has been deployed in the South China Sea, where its patrol will reaffirm that waters there are for international use. Beijing claims ownership of the lucrative area

In his confirmation hearing last month, Rex Tillerson sparked talk of war when he said he wanted to stop China from accessing islands in the sea that it has militarized

The USS Carl Vinson aircraft carrier group is engaging in 'routine operations in the South China Sea,' the navy said in a statement.

It noted that the ships and aircraft had recently conducted exercises off Hawaii and Guam to 'maintain and improve their readiness and develop cohesion as a strike group.'

'We are looking forward to demonstrating those capabilities while building upon existing strong relationships with our allies, partners and friends in the Indo-Asia-Pacific region,' strike group commander Rear Admiral James Kilby said.

The group will patrol an area that has seen China butting heads with neighboring countries including the Philippines, Vietnam, Malaysia and Brunei over ownership.

The Chinese foreign ministry has said ships and aircraft are allowed to operate in the area according to international law.

But on Wednesday, as reports that the Vinison was heading to China first emerged, a Beijing spokesman 'urged' the US to respect the region's 'efforts to maintain peace and stability in the South China Sea'.

Beijing 'firmly opposes any country's attempt to undermine China's sovereignty and security in the name of the freedom of navigation and overflight,' he said.

Concerns about a possible US-China conflict were raised in at the start of the month when a recording emerged of Steve Bannon, Trump's closest aide, saying that he expected a war with China within ten years.

'We're going to war in the South China Sea in five to 10 years, aren't we?' Bannon said on his radio show in March 2016, according to The Independent.

China has artificially built up islands into military bases. It challenges Vietnam, Malaysia, the Philippines and Burma for the sea. Left: An island in 2014; right: same island, 2015

This is the island in 2016. Tillerson's remarks caused the Chinese army to say the possibility of war with the US was a 'practical reality' and state media to talk of 'nuclear strategy'

'There's no doubt about that. They're taking their sandbars and making basically stationary aircraft carriers and putting missiles on those.

'They come here to the United States in front of our face - and you understand how important face is - and say it's an ancient territorial sea.'

Just days before that report, the People's Liberation Army (PLA) had posted a message on its website saying that war with America was becoming a 'practical reality'.

'"A war within the president's term" or "war breaking out tonight" are not just slogans, they are becoming a practical reality,' the PLA said, according to the independent Hong-Kong-based newspaper The South China Morning Post.

And last month, a report in the Global Times, a state media publication that represents the more hawkish wings of the Chinese government, talked of a possible 'military clash' with the US that would require a 'nuclear strategy'.

'The US has no absolute power to dominate the South China Sea,' the editorial, published without a byline, said.

'[Secretary of State Rex] Tillerson had better bone up on nuclear power strategies if he wants to force a big nuclear power to withdraw from its own territories.

'If Trump's diplomatic team shapes future Sino-US ties as it is doing now, the two sides had better prepare for a military clash.'

Both that editorial and the PLA's remarks came in response to Tillerson's remarks that China should be stopped from accessing the islands that it has been militarizing over the past several years.

Trump's closest adviser, Steve Bannon (right) said in 2016 that he believed war with China over the islands was 'five-to-ten years' away

Rex Tillerson met with Chinese counterpart Wang Yi (right) at a G20 meeting on Friday, cooling the situation. But the Vinison's voyage in the sea will not help tensions

'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,' Tillerson said.

He made the remarks in his confirmation hearing, in which he likened the expansion of China's influence to Russia's annexation of Crimea.

'We're going to have to send China a clear signal that, first, the island-building stops,' Tillerson said. 'And second, your access to those islands also is not going to be allowed.'

Fires were dampened somewhat on Friday as Tillerson met Chinese foreign secretary Wang Yi at a G20 gathering.

Wang told the secretary that the US and China share more similarities than differences.

But the arrival of the Vinison will do little to help tensions.

The Vinson has deployed to the South China Sea 16 times in its 35-year history, the US Navy said.

Washington says it does not take sides in the territorial disputes, despite sending in warships and planes to assert freedom of navigation in the sea several times.