With North Korean leader Kim Jong Un on an armoured train barrelling through China toward Vietnam's capital, and US President Donald Trump about to board a jet for Hanoi, Vietnamese officials scrambled on Monday to finish preparations for a rushed summit that will capture global attention.

Officials in Hanoi said they had about 10 days to prepare for the summit — much less than the nearly two months they said Singapore was given for the first Trump-Kim meeting last year— but still vowed to provide airtight security for the two leaders.

'Security will be at the maximum level,' Vietnamese deputy minister of foreign affairs Le Hoai Trung told reporters at a briefing meant to showcase the nation's efforts to welcome Kim and Trump.

Another official, Nguyen Manh Hung, the leader of the information ministry, said the 3,000 journalists from 40 countries expected in Hanoi could rely on his agency as 'you'd count on a family member'.

The world will be watching as Trump and Kim deal with one of Asia's biggest security challenges: North Korea's pursuit of a nuclear programme that stands on the verge of viably threatening any target on the planet.

Although many experts are sceptical that Kim will give up the nukes he likely sees as his best guarantee of continued rule, there was a palpable, carnival-like excitement among many in Hanoi as the final preparations were put in place.

T-shirts were being sold bearing Kim's face along with the phrase 'Rocket Man,' a nod to the insulting nickname Trump gave Kim in 2017, when North Korean weapons tests and back-and-forth threats by the leaders had many fearing war.

Kindergarteners dressed in traditional Korean Hanbok were practicing songs meant to welcome Kim. Grinning tourists were posing in front of the hundreds of US and North Korean flags around the city.

The ultra-tight security will be appreciated by North Korean authorities, who are extremely vigilant about the safety of Kim, the third member of his family to rule the North with absolute power. Kim's decision to take a train, not a plane, may have been influenced by better ability to control security. When Kim flew to Singapore, North Korea borrowed a Chinese plane.

Vietnam is eager to show off its huge economic and development improvements since the destruction of the Vietnam War, but the country also tolerates no dissent and is able to provide the kind of firm hand not allowed by more democratic potential hosts.

Take the reaction to two men impersonating Kim and Trump who'd been posing for pictures with curious onlookers ahead of the summit.

Last week, the Kim lookalike, whose name is Lee Howard Ho Wun, posted on Facebook that about 15 police or immigration officers demanded a mandatory 'interview' and threatened him with deportation. He said officials later told him that his visa was invalid and he had to leave the country.

'I feel a little bit annoyed,' the Hong Kong-based impersonator, who uses the name Howard X, said as he checked out of his hotel. 'But what is to be expected of a one-party state with no sense of humour?'

Vietnam has also announced an unprecedented traffic ban along a possible arrival route for Kim. The Communist Party's Nhan Dan newspaper quoted the roads department as saying the ban will affect the 169-kilometer (105-mile) stretch of Highway One from Dong Dang, on the border with China, to Hanoi.

Hundreds of soldiers guarded the area near the Dong Dang railway station on Monday ahead of Kim's expected arrival. Kim may get off his train in Dong Dang and finish his journey to Hanoi by car.

There are high expectations for the Hanoi summit after a vague declaration at the first meeting in June in Singapore that disappointed many.

In a meeting with senior aides in Seoul, South Korean President Moon Jae-in said Monday that the Trump-Kim talks would be a critical opportunity to achieve peace on the Korean peninsula.

Moon, who met Kim three times last year and has lobbied hard to revive nuclear diplomacy between the US and North Korea, is eager for a breakthrough that would allow him to push ambitious plans for inter-Korean engagement, including lucrative joint economic projects that are held back by US-led sanctions against the North.

'If President Trump succeeds in dissolving the world's last remaining Cold War rivalry, it will become yet another great feat that will be indelibly recorded in world history,' Moon said.

Trump, via Twitter, has worked to temper those expectations, predicting before leaving for Hanoi a 'continuation of the progress' made in Singapore but adding a tantalising nod to 'Denuclearisation?'

He also said that Kim knows that 'without nuclear weapons, his country could fast become one of the great economic powers anywhere in the world'.

North Korea has spent decades, at great political and economic sacrifice, building its nuclear program, and there is widespread skepticism among experts that it will give away that program cheaply.

South Korean media have reported that Trump and Kim might strike a deal that stops short of a hoped-for roadmap for full North Korean denuclearisation.

US secretary of state Mike Pompeo said on Fox News Sunday that he was hoping for a 'substantive step forward'. He cautioned, 'it may not happen, but I hope that it will.'