Donald Trump on Tuesday said he would speak with North Korean leader Kim Jong-Un, in what would be a dramatic shift in US policy.

"I would speak to him, I would have no problem speaking to him," the Republican presumptive presidential nominee told Reuters in an exclusive interview.

Until now, the US strategy has been to try and isolate Pyongyang.

"I would put a lot of pressure on China because economically we have tremendous power over China. People don't realize that," Trump added, talking about China as North Korea's lone ally.

"They are extracting vast billions of dollars out of our country. Billions. And we have tremendous power over China. China can solve that problem with one meeting or one phone call."

Asked how that could unfold, Trump said: "Because they have tremendous power over North Korea."

Reminded that North Korea has nukes, Trump replied: "I know that. So does China, by the way."

The Republican also called for a renegotiation of the Paris climate accord, saying he is "not a big fan," and voiced disapproval of Russian President Vladimir Putin's moves in eastern Ukraine, the report said.

The Paris deal stipulates agreed carbon emissions reductions by more than 170 countries. He said he would want to renegotiate the deal because it treats the United States unfairly and gives favorable treatment to countries such as China.

"I will be looking at that very, very seriously, and at a minimum I will be renegotiating those agreements, at a minimum. And at a maximum I may do something else," Trump said.

Reworking or scrapping the pact would be a big setback for what was touted as the first global climate pact.