Trump left Washington DC about 12.30pm local time on Monday and is scheduled to arrive in Vietnam on Tuesday evening, Vietnam's foreign ministry says.
The two leaders are due to meet in the Vietnamese capital Hanoi on Wednesday and Thursday, eight months after their historic summit in Singapore, the first between a sitting US president and a North Korean leader.
On Wednesday morning, Trump is set to meet Vietnam President Nguyen Phu Trong, the ministry said.
Vietnam has released few details about arrangements for the summit including its specific venue or timing.
Kim is making his way to Vietnam by train and passed through the Chinese city of Hengyang at 3.30pm local time on Monday, South Korea's Yonhap news agency reported.
