Trump said: "This is a great opportunity for peace, and lasting peace, and prosperity.

"So we're going in with a very positive attitude, and I think we're going to come out fine."

But he cautioned that there's a good chance it won't work out. "There's probably an even better chance that it will take a period of time. It will be a process," he said.

The US president has in the past week tamped down the previous high expectations of a rapid complete, verifiable and irreversible denuclearization on the part of the DPRK. He has since described the first summit as a get-to-know-you meeting, and that denuclearization will take many meetings.

"I think the minimum would be a relationship. You'd start at least with a dialogue," Trump said.

Kim did not make public statement before or after his arrival in Singapore. He met Singaporean Prime Minister Lee Hsien Loong on Sunday evening. Trump will meet Lee on Monday.