China to send envoy to North Korea

China is set to dispatch a special envoy to North Korea on Friday, a trip hailed as a "big move" by US President Donald Trump, who has urged Beijing to pile pressure on its nuclear-armed ally.

Song Tao is officially travelling to the North to brief officials on the recent Chinese Communist Party congress and "other issues of mutual concern" on behalf of President Xi Jinping.

But analysts expect Song to address the nuclear standoff, which has roiled relations between the two Cold War-era allies as China has backed United Nations sanctions on North Korea over its missile tests and sixth nuclear blast.

Trump, who warned Xi during his trip to Beijing last week that time was "quickly running out" to solve the nuclear crisis, took to Twitter on Thursday to hail the mission as "a big move, we'll see what happens!".

The US leader wants China, which accounts for 90 percent of North Korea's foreign trade, to put more economic pressure on the reclusive regime.

But experts do not believe Song's visit will yield major breakthroughs.

"We can expect some face-saving, assuring but very general and abstract commitments with no substance changes in North Korea's nuclear and missile programmes," said Yuan Jingdong, a specialist in Asia-Pacific security issues at the University of Sydney.

The visit is "more about warning North Korea against going to extremes than forcing it to give up the nukes" because China's top priority remains maintaining regional stability, he said.

Song would likely "assure Kim that if he behaves within a reasonable bound he can expect Beijing to continue providing some assistance and resist broadening the sanctions," Yuan said.

China has imposed its own banking restrictions on North Koreans in addition to enacting a series of UN measures that include bans on imports of coal, iron ore and seafood from the North.

But Beijing fears that squeezing Pyongyang too hard would cause its collapse.

Song will be the first Chinese envoy to make an official trip to North Korea since October 2016, when vice foreign minister Liu Zhenmin visited.

'Tense situation'

China's relations with North Korea are currently at "the lowest point they've been in history," leaving the North diplomatically at its most isolated, said Lu Chao, director of the North Korea Research Centre at the Liaoning Academy of Social Sciences.

As a high-level diplomat, Song would likely meet directly with North Korea's top leaders, he said.

"As far as North Korea is concerned, China's opinion is still an important one and will certainly arouse their full attention," Lu said.

As nuclear tensions have soared Xi has pushed for negotiations and a "dual track approach" in which the United States would freeze its military drills in the region while North Korea halts its weapons programmes.

Trump claimed this week that Xi had agreed to drop his plan during their talks last week, but Beijing stood by its policy.

"It can not only ease the current tense situation, but also solve the most pressing security concerns for all parties, provide opportunities and create conditions for resuming peace talks and find breakthrough to get out of the stalemate," foreign ministry spokesman Geng Shuang said on Thursday.