Kim Jong Un is taking a laborious 3.5-day train ride to meet Trump in Vietnam, and it could be because he's too embarrassed to borrow a plane from China

• North Korean leader Kim Jong Un is in the middle of a three-and-a-half-day train trip to Hanoi, Vietnam, where he will meet US President Donald Trump for their second summit.
• Experts say his reason for taking such a slow means of transport may be to show he is not overly reliant on China.
• Kim took an Air China plane to the first Trump summit in Singapore, which led to commentary emphasising his inability to fly himself there.
• Those comments reportedly didn't sit well with Kim.

North Korean leader Kim Jong Un is taking a 2,000-mile, three-and-a-half day train ride to meet US President Donald Trump in Vietnam this Wednesday, likely to save face because he doesn't want to ask China to lend him a plane.

Kim boarded his family's armored train from Pyongyang Station on Saturday evening, and plans to arrive in Hanoi on Tuesday, the day before his summit with Trump.

Kim crossed into Dandong, a Chinese city bordering North Korea, via bridge on late Saturday, the Associated Press reported. The rest of the trip will take him through southeastern China before he eventually arrives in Hanoi.

Read more: Take a tour of the closest Chinese city to North Korea - the nearest thing to the outside world most North Koreans will ever see

He passed by the southeastern Chinese city of Hengyang around Monday afternoon local time, South Korea's Yonhap news agency reported.

According to INSIDER's calculations, the entire trip will be at least 2,000 miles long.

The specifics of his trip are not clear. Citing Vietnamese officials, The New York Times reported on Sunday that Kim will leave his train at China's border with Vietnam and travel the last 105 miles or so to Hanoi by car.

While Kim's laborious, three-day-long train ride will undoubtedly give him a good look at China's cities and countryside, experts say his reason for the journey is more likely pride than tourism.

Last year, Kim borrowed a Boeing-747 plane from the Air China, majority-owned by the Chinese state, to get himself to to Singapore for his first summit with Trump last year.

His 40-year-old, Soviet-made Ilyushin Il-62 plane was deemed unsafe for the voyage at the time.

Kim's use of a Chinese plane last year highlighted his apparent reliance on Beijing, which didn't have any delegates at Singapore but saw its global vision dominant at the summit.

The North Korean leader did not appreciate remarks about his reliance on China last year, Cheng Xiaohe, a North Korea expert at Beijing's Renmin University, told The New York Times.

Cheng told The Times: "He does not want to show the world his heavy reliance on China by waving his hand in front of China's national flag on a Chinese plane as he did at the Singapore airport."

"Traveling by train is a forced choice."

It's not clear what mode of transport Kim will take home.

Read more: Kim Jong Un rode his personal armored train to China to spend his 35th birthday with Xi Jinping

Trump has characterized the upcoming summit as a follow-up to their first meeting last June, during which Kim made a vague pledge to work toward denuclearization. Pyongyang appears not to have made much progress on this front.

US intelligence and North Korea experts have warned that Pyongyang is unlikely to give up its nuclear arms. An intelligence report published last month said the country's leaders view nuclear arms as "critical to regime survival."

Trump has repeatedly played down hopes for any new breakthroughs with North Korea, and told the Governors' Ball on Sunday that he was "not pushing for speed" with North Korea's denuclearization.

"I'm not in a rush. I don't want to rush anybody," he said. "I just don't want testing. As long as there's no testing, we're happy."

He added that US sanctions on North Korea would remain for the time being. Beijing has been urging the United Nations to relax some of its sanctions on North Korea for months.