The USS Carl Vinson will make a four-day port call to the central city of Danang for a highly symbolic trip that will include a visit to a centre for victims of Agent Orange, the toxic defoliant sprayed over large swathes of land by the US during the war.

But continuing tensions in the South China Sea loom over the trip as Beijing continues to build artificial islands capable of hosting military installations -- much to the chagrin of Vietnam and other claimants to the sea.

Though the US is not a claimant to the resource-rich waterway, through which $5 trillion in trade passes annually, it has long lobbied for freedom of navigation there to counter China's growing influence.

"This visit marks an enormously significant milestone in our bilateral relations and demonstrates US support for a strong, prosperous and independent Vietnam," Pentagon spokesman Colonel Rob Manning told reporters.

The US and Vietnam have seen an extraordinary turnaround in relations since the end of the war in 1975.

Hailing the "dramatic progress" in that relationship, US ambassador Daniel Kritenbrink said the visit underscored US commitment to the region and to Vietnam in particular.

"The United States and Vietnam share a range of interests including a desire to maintain peace, prosperity, unimpeded commerce, (and) freedom of navigation, upon which the region and its economies depend," he told reporters Monday.

Though US military ships have regularly docked in Vietnam in recent years, this is the first port call for an aircraft carrier. It will anchor just off Danang, where US Marines landed 53 years ago this month -- the first direct involvement by American combat troops in the war.

Ties between the wartime enemies have warmed in recent years, especially under former US President Barack Obama, who in 2016 lifted a decades-old arms embargo.

President Donald Trump has insisted he will remain engaged in Asia, but his strategy has been led by his "America First" clarion call, insisting that Vietnam buy more military equipment from America and reduce its yawning trade deficit.

One of Trump's first acts in office was withdrawing from the 12-member Trans-Pacific Partnership trade pact, from which Vietnam stood to gain enormously.

- Military might -

Analysts say the port call, which follows a visit to the Philippines last month, is a chance for the United States to flex its military muscle in Asia.

"It's a US push... to demonstrate a massive naval presence in the South China Sea area to China, that the US is staying engaged," Vietnam expert Carl Thayer told AFP ahead of the trip.

US officials refused to be drawn on the tensions with China on Monday, insisting the trip was a routine deployment to the Western Pacific.

"In terms of our mission, it's the same thing that the mission has always been, of promoting peace and prosperity and stability in the region. I'm not going to speak specifically to China," Rear Admiral John Fuller, commander of the Carl Vinson strike group, told reporters Monday.

Compared to the 11 active aircraft carriers in the US Navy, China currently boasts just one. But it has made no secret of its desire to build up its naval forces and become much more regionally assertive.

Vietnam remains the most vocal claimant in the South China Sea dispute as the Philippines has backed off under China-friendly President Rodrigo Duterte. Taiwan, Malaysia and Brunei also have claims.

The Filipino leader has refused to pursue a landmark 2016 international tribunal ruling in Manila's favour over its competing claims with Beijing.

"The Philippines has just rolled over, China is continually militarising and if the US doesn't maintain a presence in the region, Vietnam's got nowhere to hide," Thayer said.

Vietnam has always insisted that it is committed to maintaining peace and stability in the region and calls for freedom of navigation laws to be respected, though it rarely names Beijing.

The nuclear-powered USS Carl Vinson, home to some 5,000 sailors and 72 aircraft, regularly deploys to the Indo-Pacific region. The 1,000 foot-long (300 metre) ship weighing 95,000 tons will be in Danang until its departure on Friday.

The visit includes a number of cultural and community events, such as basketball and soccer matches between US sailors and locals, an orphanage visit and naval band concerts.