North Korea 'could be great power' without nuclear weapons: Trump

North Korea could become one of the world's 'great economic powers' if it relinquishes its nuclear weapons, United States President Donald Trump has said on the eve of his departure for Vietnam for a second summit with North Korean leader Kim Jong Un.

Trump's comments came hours after Secretary of State Mike Pompeo said Pyongyang remains a nuclear threat.

Trump will meet North Korean leader Kim Jong Un for the second time on the 27-28 February in Hanoi, Vietnam.

'We both expect a continuation of the progress made at first summit in Singapore,' Trump tweeted, referencing the meeting between the two leaders in Singapore last June.

Trump and Kim had their historic first meeting in Singapore last June, wherein they agreed on denuclearisation of North Korea.

North Korea has long insisted it will not give up its nuclear arsenal unless the US removes its troops from South Korea.

"...I tell Chairman Kim, he has a chance to have a country that is so vibrant, economically. Maybe one of the most in the world. He's got a location that's unbelievable.

"As a real-estate person, I've always done very well with location. But he's right between China, Russia, and then on the other side, South Korea. So they can't touch each other unless they go through North Korea," Trump told a meeting of Governor's at the White House.

"And I think it can be, really, one of the great -- one of the great financial and economic countries anywhere in the world.

"So I tell him that. I said, 'But you can't do that if you're going to keep nuclear. If you do nuclear, that can't ever happen'," Trump said.

Trump reiterated that he is having a great relationship with Kim.

Trump said he was 'not in a rush' to denuclearise North Korea.

"We see eye to eye, I believe. But you'll be seeing it more and more over the next couple of days, one way or the other.

"What's going to happen? I can't tell you. I think eventually it would, but I can't tell you. And I'm not in a rush. I don't want to rush anybody.

"I just don't want testing. As long as there's no testing, we're happy,” he said.

Trump said he has 'done really something, very special' with respect to North Korea.