South Korean President Moon Jae-In will meet with his Chinese counterpart Xi Jinping in Beijing today amid mixed US signals about potential talks to resolve the North Korean nuclear crisis.

Relations between Beijing and Seoul have encountered their own rough patch over the US military's deployment of a powerful anti-missile defence system in the South to counter the North's threats.

Moon hopes to "normalise" ties during the visit, his office has said, after Beijing imposed economic measures against South Korean companies, a move seen as retaliation to the installation of the THAAD (Terminal High Altitude Area Defense) system.

China sees the deployment as a threat to its own security.

Moving past the disagreement has become increasingly important amid growing concern that bellicose rhetoric between Washington and Pyongyang could spark war on the Korean peninsula.

"The highlights to watch of the visit would be whether the two sides (Seoul and Beijing) can start a dialogue and cooperation mechanism on the DPRK (North Korea) nuclear issue," said Zhu Feng, international studies professor at Peking University.

China has long refused to countenance the possibility that the North's Communist regime could collapse.

But a series of nuclear and missile tests combined with pressure from US President Donald Trump has pushed Beijing to reconsider its position and prioritise improving relations with Seoul.

"It is a very uncertain period," Zhu said. "The two sides need high-level dialogues and dialogues between militaries.

These dialogues cannot really start without the normalisation of the bilateral relations." 

Moon's visit comes after US Secretary of State Rex Tillerson said Washington was ready to talk to North Korea "without preconditions", though it remains determined to force Pyongyang to give up its nuclear arsenal.

China and Russia responded positively to Tillerson's remarks, even after the White House appeared to put his proposal in question by saying Trump's "views on North Korea have not changed." 

Beijing has pressed for talks to peacefully resolve the crisis, but there are signals that it has begun to prepare for the possibility of the North's collapse.

Tillerson said Tuesday that US and Chinese officials have discussed scenarios in case the North Korean regime falls, including steps to deal with refugees crossing the border, and how to secure Pyongyang's nuclear weapons.

Washington's top diplomat said these discussions involved him, the US defence secretary and military chief, and senior Chinese officials.

Such discussions were unthinkable just a few months ago.

But China's priority has been to convince the United States and North Korea to hold talks.

Beijing has also urged the US, Japan and South Korea to suspend joint military drills in the region in return for North Korea to halt its nuclear activities -- an idea consistently rejected by Washington and Seoul.