On historic North Korean anniversaries Kim regularly pays tribute to his predecessors, his father Kim Jong Il and grandfather Kim Il Sung, at the mausoleum on the outskirts of Pyongyang where their preserved remains lie in state.

But his stop at the stark concrete monument where the body of Vietnam's independence hero is on display was unusual.

The North Korean leader adjusted the ribbons on a large wreath emblazoned with his name and the message "Cherishing the memory of President Ho Chi Minh", before bowing his head for almost a minute.

He is not known to have made a similar visit to Mao Zedong's mausoleum in Beijing during any of his four visits to China, the North's key diplomatic protector and main provider of trade and aid.

But North Korean founder Kim Il Sung was a close friend of Ho Chi Minh, supplying him with fighter pilots and psychological warfare specialists during his war against the US-backed regime in South Vietnam.

Pictures of the two together are displayed on the noticeboard outside the Vietnamese embassy in Pyongyang.

Kim's trip is the first by a North Korean leader since 1964, when Kim Il Sung also travelled by rail for his journey to the southeast Asian nation.

Kim Jong Un was due to board his own armoured olive green train later Saturday for the 4,000-kilometre (2,500-mile) marathon back through China to Pyongyang.

Kim and Trump's much-hyped second summit finished abruptly with a scrapped signing ceremony after the pair failed to reach an agreement on walking back North Korea's nuclear programme.