'One time shot' for peace with North Korea: Trump

US President Donald Trump said his summit with North Korea represented "a one-time" chance to forge peace and that he would know within a minute if his counterpart Kim Jong Un was a serious partner.

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.

In Singapore, police, including elite units of Nepalese Gurkhas, are poised to flood the streets and enforce a virtual lockdown of key sections of the city, blocking off roads to facilitate the historic face-to-face between Trump and Kim Jong Un.

And in order to preempt any disruptive protests, a blanket ban has been imposed on bringing flares, banners or loudhailers anywhere near the key summit venues.

Concrete barricades will spring up at key sites and mechanical metal barriers that rise from the ground at the touch of a button are likely to appear on some roads.

Authorities have also restricted the use of airspace, apparently to allow Kim, Trump and their entourages to get in and out of the city-state smoothly.

But that could spell problems for travellers using Singapore's Changi Airport -- one of the world's busiest international hubs -- with aviation authorities warning of delays.