US president Donald Trump and North Korea's Kim Jong Un have cut short their second summit without reaching an agreement.

White House press secretary Sarah Sanders said the leaders had a "very good and constructive meeting" and discussed ways to advance "denuclearisation and economic-driven concepts".

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She said their teams "look forward to meeting in the future".

Both leaders' motorcades roared away from the downtown Hanoi summit site within minutes of each other after both a lunch and a signing ceremony were scrapped.

Mr Trump's end-of-summit news conference was moved up and White House aides said he would address the sudden change in plans.

The breakdown came just hours after Mr Trump and Mr Kim appeared to inch toward normalising relations between their still technically-warring nations.
In something of a role reversal, Mr Trump deliberately ratcheted down some of the pressure on Pyongyang, abandoning his fiery rhetoric and declaring he was in "no rush. We just want to do the right deal".

Mr Kim, for his part, when asked whether he was ready to denuclearise, said: "If I'm not willing to do that I won't be here right now."

Furthering the spirit of optimism, the leaders seemed to find a point of agreement moments later when Mr Kim was asked if the US may open a liaison office in North Korea.

Mr Trump declared it "not a bad idea" and Mr Kim called it "welcomable".

But questions persisted throughout the summit, including whether Mr Kim was willing to make valuable concessions, what Mr Trump would demand in the face of rising domestic turmoil and whether the meeting could yield far more concrete results than the leaders' first summit, a meeting in Singapore less than a year ago.

There had long been scepticism that Mr Kim would be willing to give away the weapons his nation had spent decades developing and Pyongyang felt ensured its survival.

Mr Trump had signalled a willingness to go slow: After painting the threat from Pyongyang as so grave that "fire and fury" may need to be rained down on North Korea, Mr Trump made clear he was willing to accept a more deliberate timetable for denuclearisation.

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"I can't speak necessarily for today, Mr Trump said, "but... over a period of time I know we're going to have a fantastic success with respect to Chairman Kim and North Korea."

In an unexpected development, Mr Kim on Thursday fielded questions from Western journalists for likely the first time, with the reporters receiving some coaching from the US president, who implored, "Don't raise your voice, please. This isn't like dealing with Trump."

The North Korean leader struck a largely hopeful note, saying "I believe by intuition that good results will be produced."

After a reporter asked Mr Kim if they were discussing human rights, Mr Trump interjected to say they were "discussing everything", though he did not specifically address the issue.

Earlier, accompanied only by translators, the unlikely pair - a 72-year-old brash billionaire and a 35-year-old reclusive autocrat - displayed a familiarity with one another as they began the day's negotiations.

After a 40-minute private meeting, the leaders went for a stroll on the Hotel Metropole's lush grounds, chatting as they walked by a swimming pool before being joined by aides to continue talks.

"The relationship is just very strong and when you have a good relationship a lot of good things happen," said Mr Trump.

He added that "a lot of great ideas were being thrown about" at their opulent dinner the night before.

"I believe that starting from yesterday, the whole world is looking at this spot right now," Mr Kim said via his translator.

"I'm sure that all of them will be watching the moment that we are sitting together side by side as if they are watching a fantasy movie."

Possible outcomes that had been considered were a peace declaration for the Korean War that the North could use to eventually push for the reduction of US troops in South Korea, or sanctions relief that could allow Pyongyang to pursue lucrative economic projects with the South.