That first historic summit in Singapore produced little more than a vaguely worded document committing to "complete denuclearisation" and observers say concrete steps will need to be laid out at their second meeting in Hanoi.

But Trump appeared to temper expectations of any major breakthroughs, telling reporters Thursday he was "in no rush", saying results would be achieved over the longer term.

"We are going to see, there is no rush, we want to do the right deal," he said as he sat down with Kim at the luxury Metropole hotel.

For his part, Kim promised to "do my best to achieve a great, ultimately good outcome."

They had "walked side by side to Hanoi", where the summit was taking place, and were "continuing great dialogue", he added.

The leaders are scheduled to meet face-to-face this morning before signing a declaration at 2:00 pm (0700 GMT) today.

Trump will hold a press conference before leaving Vietnam Thursday evening, while Kim will stay on for a state visit until his departure this weekend.