There has also been ratcheted up rhetoric from the USA and Pyongyang, with the latter's state media warning Thursday that a pre-emptive strike by North Korea would result in the US and South Korea being "completely destroyed in an instant".
"We are closely watching the situation", he said, adding that South Korea would not let its guard down.
However, China's defence ministry yesterday said Chinese forces on the country's border with North Korea maintained a state of normal combat preparedness and training.
US and South Korean officials have been saying for weeks that the North could soon stage another nuclear test in violation of United Nations sanctions, something both the United States and China have warned against.
Such a contingency could include the risk of an armed conflict breaking out as tensions on the peninsula have risen in the wake of multiple North Korean missile tests.
Even as the USA government continues to warn North Korea to take a more soft lined approach to the festering disagreements with South Korea and the US itself, the latter has not given any indication that it is willing to do so.More news: Mark Selby in control against Fergal O'Brien at World Snooker Championship
Top envoys from the US, South Korea and Japan are due to meet on Tuesday, South Korea's foreign ministry said, to "discuss plans to rein in North Korea's additional high-strength provocations, to maximise pressure on the North and to ensure China's constructive role in resolving the North Korea nuclear issue".
A North Korean missile blew up nearly immediately on its test launch on Sunday, the USA military said.
South Korea's Ministry of Foreign Affairs also balked at the error. South Koreans have largely welcomed Trump's hardline stance on North Korea, but some have expressed frustration over his public gaffes. "I think at the end of the day we realized North Korea is a problem and no one on the council wants to see North Korea move forward with any sort of testing or strikes. and if we have to start looking at sanctions or other actions we will".
The comments to Reuters came before U.S. President Donald Trump on Thursday cited, without explanation, "some very unusual moves" that he said had been taken over the last two or three hours.
An official Chinese newspaper said there was optimism about persuading North Korea to end its pursuit of a nuclear programme without the use of force, "now that even the once tough-talking Donald Trump is onboard for a peaceful solution".
The North has said it has developed a missile that can strike the mainland United States, but officials and experts believe it is some time away from mastering the necessary technology, including miniaturising a nuclear warhead.