Speaking shortly before beginning his long journey to Singapore, Trump told reporters that contacts between the US and North Korean negotiators had been positive in the build-up to Tuesday's historic meeting and talked up its prospects of success.

"It's unknown territory in the truest sense but I really feel confident," Trump said as he prepared to leave the ongoing G7 summit in Canada early and head to Asia.

"I feel that Kim Jong Un wants to do something great for his people and he has that opportunity... It's a one-time shot," he said at a press conference, adding that the North Koreans had been working "very well with us" ahead of the summit.

Trump and Kim are due to have the first ever US-North Korea summit in Singapore on Tuesday, with the American leader hoping his counterpart will scrap his nuclear weapons program in return for security guarantees.

The US president is the first of the G7 leaders to leave the summit in Canada where he has briefed his peers on the meeting.

"I am on a mission of peace and we're going to be carrying the hearts of millions of people from all," he said.

"We have to get denuclearization, we have to get something going."

Asked how long it would take for him to work out if Kim was serious about striking some kind of peace deal, Trump replied: "I think within the first minute I'll know.

"I think I'll know pretty quickly whether or not, in my opinion, something positive will happen. And if I think it won't happen, I'm not going to waste my time. I don't want to waste his time."