Beijing is North Korea's sole major ally and Kim travelled for more than two days by train across China on his way to Hanoi.

The North Korean leader met with Chinese President Xi Jinping for a fourth time in January, showing that Beijing retains a key role in the diplomatic shuffle.

"In this Hanoi meeting, we can not only increase the hard-won warming up of the situation, but we can also take an important step towards advancing the denuclearisation of the peninsula and establishing a peace mechanism," Foreign Minister Wang Yi said after talks with his Russian and Indian counterparts in the eastern Chinese city of Wuzhen.

Trump was due to meet Kim for dinner later Wednesday and meet again on Thursday.

Following a historic first meeting in Singapore in June that produced a vaguely worded statement about denuclearisation, analysts say the second summit in Vietnam's capital Hanoi must this time put substance ahead of bonhomie.