A convoy carrying at least two of Kim's top aides, both of them vice-chairmen of North Korea's ruling Workers' Party, visited the Vinfast complex in Vietnam's coastal industrial hub of Haiphong.

The long motorcade rolled past lines of people in Vinfast jackets waving Vietnamese and North Korean flags.

The trip came after Trump, in a morning tweet, touted an "AWESOME" future for North Korea if it gives up its nuclear weapons, and held up rapidly growing Vietnam as an example.

Vinfast is the Communist country's first homegrown car manufacturer and part of its largest private conglomerate -- owned by the country's richest man, multi-billionaire Pham Nhat Vuong.

The firm unveiled its first two models, a sedan and an SUV, at the Paris Auto Show in November with former footballer David Beckham brought in to promote the cars.

Using technology licensed from German giant BMW and designed by Italian firm Pininfarina -- which counts Ferrari among its customers -- they are projected to go on sale in September.

Production has yet to begin, but Vinfast has poured $1.5 billion into its sprawling new factory northeast of Hanoi.

In contrast, North Korea's main car company, Pyonghwa -- originally set up by the Southern-based Unification Church -- is said to rebadge vehicles made by Chinese firms such as Dongfeng Motors.

The North Korean delegation led by senior ruling party leader Ri Su Yong toured the gleaming factory where rows of shiny motorbikes were on display.

Later the North Koreans held talks with representatives from Vingroup -- Vinfast's parent company -- before leaving the factory with a convoy of about 20 cars to visit an agricultural project owned by the conglomerate.

Earlier, the North Korean delegation went to Halong Bay, whose towering rocky karsts are the crown jewels of Vietnam's tourism sector.

Kim himself remained in his Hanoi hotel for the day as he prepared for his face-to-face meeting and dinner with Trump later Wednesday.

The North has sought to develop its nascent tourism sector, with Kim overseeing the development of the giant Wonsan-Kalma resort project under construction on its east coast.

- 'Learn a lot' -

Like China, Vietnam's Communist authorities have embraced market economics in recent decades and have been rewarded by a glittering economic transformation.

Expansion has largely been buoyed by the low-cost manufacture and export of goods from Nike shoes to Intel processors, and today it is one of Asia's fastest-growing economies with GDP rising 7.08 percent last year.

Vingroup CEO Vuong started out in business selling dried noodles in Ukraine, and has grown his empire to become Vietnam's biggest conglomerate.

It owns a string of holiday resorts, luxury condominiums, shopping malls, convenience stores, schools, hospitals and farms across the country, with Forbes estimating Vuong's net worth at $7.8 billion.

Koh Yu-hwan, a professor of North Korean Studies at Dongguk University, told AFP that Vietnam was "an ideal country to benchmark for North Korea" as it was "also a socialist country that has achieved significant economic growth through reform".

"But it will be hard for North Korea to adopt Vietnam's model," he added.

Pyongyang has quietly been reforming its sanctions-hit economy for years, loosening the shackles on state-owned enterprises and turning a blind eye to private business activities, but the state retains a significant role.

And it has a mountain to climb -- its infrastructure is ramshackle, electricity supplies are intermittent, and several past foreign investments have failed.

The North would want a state-led development strategy controlled by the authorities, Koh said. But Vietnam's growth has been fuelled by foreign investment from firms such as South Korean telecoms giant Samsung, which has poured in billions of dollars.

That "will not work for North Korea", Koh said. But it could still "learn a lot from Vietnam", which was achieving rapid growth "while maintaining its socialist system".

Going to one of Samsung's plants in Vietnam was politically impossible for Kim, he said, but "visiting the Vinfast plant makes sense since it's Vietnam's success model through a traditional Vietnamese method."

"That is what North Korea wants -- success through a North Korean model."