US President Donald Trump said on Wednesday that he hoped his May or early June summit with Kim Jong-un, top leader of the Democratic People's Republic of Korea, would lead to lasting peace on the Korean Peninsula.

"I hope to have a very successful meeting (with Kim)," Trump said at his Mar-a-Lago retreat in Florida during a joint news conference with visiting Japanese Prime Minister Shinzo Abe.

"We hope to see the day when the whole Korean Peninsula can live together in safety, prosperity and peace."

China's Foreign Ministry said Beijing welcomed the direct contacts and talks between the US and the DPRK and hopes their dialogue will go smoothly and achieve a positive outcome.

"We hope that all relevant parties will begin and continue with their talks, accumulate mutual trust and build up consensus," Foreign Ministry spokeswoman Hua Chunying told a news conference in Beijing.

"We expect them to follow the 'dual track' approach to advance the political settlement process of the Korean Peninsula issue, so as to promote and achieve the denuclearization on the one hand and establish the peace regime of the Peninsula on the other hand."

Hua also said that as a close neighbor in the Peninsula, China is willing to continue its constructive role in promoting the settlement of issues in the region.

Trump tweeted earlier on Wednesday that a "smooth" meeting had already taken place between his CIA chief Mike Pompeo and the DPRK top leader and "a good relationship was formed", and "details of summit are being worked out now".

In his talk with the media, however, Trump reiterated that the summit might not happen.

"If I think that it's a meeting that is not going to be fruitful, we're not going to go," he said, according to Reuters. "If the meeting when I'm there is not fruitful, I will respectfully leave the meeting."

Trump and Abe said they had failed to reach a deal that would exempt Japan from new US steel and aluminum tariffs, as Abe had wanted.

Instead, they announced they had agreed to start talks on a new "free, fair and reciprocal" trade agreement following two days of talks.

Abe said that differences remained in each country's approach, Reuters reported.

"On the US side, they are interested in a bilateral deal," Abe told reporters.

"Our country's position is that TPP is the best for both of our countries," he added, referring to the Trans-Pacific Partnership trade pact.

Trump said: "I don't want to go back into TPP, but if they offered us a deal that I can't refuse on behalf of the United States, I would do it."

Reuters and AP contributed to this story.