South Korean President Moon Jae-in has urged North Korea to take bold and concrete measures to speed up denuclearisation, adding that China can continue to play a positive role in nudging Pyongyang towards that goal.

But he has also stressed the need for the United States to implement reciprocal measures to motivate the North.

The reality, however, is that neither side is willing to make the first move, resulting in a stalemate in nuclear talks. Mr Moon attributed this to years of hostility and distrust between the two countries since the 1950-53 Korean War, when the US sided with South Korea.

"Both sides know what must be done for international sanctions to be lifted... but they are asking each other to make the first move, which is why the second US-North Korea summit is delayed until now," Mr Moon said during his New Year press conference yesterday.

"They need to narrow the differences between them before their second meeting."

US President Donald Trump and North Korean leader Kim Jong Un agreed to work towards denuclearisation when they first met in Singapore in June last year.

A second summit is due early this year, and the US has reportedly scouted locations in Hanoi, Bangkok and Hawaii.

Mr Moon admitted that the first summit did not produce specific results, and the second one must delve into details of follow-up measures.

The South Korean leader, who met Mr Kim three times last year, suggested that North Korea could demolish its production line for inter-continental ballistic missiles or destroy other missile test sites.

"Then when the US implements corresponding measures, trust will be built and the denuclearisation process can move on smoothly," he said.

Mr Moon's remarks came as his North Korean counterpart returned from a trip to China.

In meetings with President Xi Jinping, Mr Kim reaffirmed his commitment to denuclearisation and producing good results from his anticipated second summit with the US, reported Xinhua news agency.

Mr Xi said joint efforts by China, the North and other relevant parties have yielded significant progress and the "political settlement of the peninsula issue faces a rare historic opportunity".

"China hopes that North Korea and the United States will meet each other halfway," he added.

Mr Scott Snyder, a senior fellow at the Council on Foreign Relations in Washington, noted that conveying "an image of solidarity with China" is the most effective way for Mr Kim to "enhance his own strategic depth and standing", while negotiating with other world leaders.

"Kim's meetings with Xi are an effort to drive up the price in negotiations with the United States beyond what North Korea would be able to demand on its own," he wrote in a blog post.

Mr Moon said he expects high-level talks to be held soon, noting that Mr Kim's visit to China is a prelude to the summit.

Last year, Mr Kim had visited China - North Korea's only ally and economic lifeline - before meeting Mr Moon and then Mr Trump.

China has played an "important and very positive role" in the denuclearisation process, and can continue to do so, said Mr Moon.

"Chairman Kim's visit to China also plays a positive role in facilitating the second US-North Korea summit."