China has warned that it will never accept North Korea as a nuclear weapons state, Beijing's ambassador to the US warned, just hours after Kim Jong-un said his country was on course to achieve that "final goal".

Speaking at a Chinese embassy event in Washington DC, Cui Tiankai also called on Donald Trump's  administration to stop sabre-rattling against the secretive communist state. 

Instead the US should "resume dialogue and negotiation" over the stand-off, he said. 

"Honestly, I think the United States should be doing much more than now, so that there's real effective international cooperation on this issue," he told reporters. 

"They should refrain from issuing more threats. They should do more to find effective ways to resume dialogue and negotiation," he said, while adding that China would never accept North Korea as a nuclear weapons state.