Kim Jong-un, top leader of the Democratic People's Republic of Korea, kicked off an official visit to Vietnam on Friday, three days after arriving in the country for a summit with US President Donald Trump which ended without a deal.

Accompanied by his sister and close aide Kim Yo-jong, he was received by Vietnamese President Nguyen Phu Trong who is also the general secretary of the Communist Party of Vietnam.

The smiling leader walked before rows of children waving Vietnamese and DPRK flags outside the Presidential Palace, before inspecting an honor guard.

Vietnam is Kim's fourth foreign destination in less than 12 months.

He has traveled to China four times for meetings with President Xi Jinping, walked across the border with the Republic of Korea for a summit with ROK President Moon Jae-in, and went to Singapore for his first summit with Trump in June.

But for protocol purposes Kim's trips do not rank as state visits, as he is not the DPRK's head of state - his grandfather Kim Il-sung retains the title of Eternal President after he died in 1994.

Instead, Kim is chairman of the ruling Workers' Party of Korea and chairman of the State Affairs Commission, although he is most widely referred to as the top leader.

The DPRK's state KCNA news agency described it as an "official goodwill visit" to Vietnam.

Onlookers lined the streets on Friday to catch a glimpse of Kimthe first DPRK leader to visit Vietnam since Kim Il-sung in 1964.

The DPRK top leader also met the Nguyen Thi Kim Ngan, chairwoman of Vietnam's National Assembly in Hanoi on Friday.

He is expected to lay wreaths at the Ho Chi Minh Mausoleum and war martyrs monument on Saturday ahead of his planned departure by train for the marathon return journey home in the evening.

Kim undertook a 4,000-kilometer rail journey through China to Vietnam to attend the summit.

AFP and Reuters contributed to this story.