The sharp language came after US President Donald Trump said the North Korea issue "will be taken care of". Trump has sent an aircraft carrier-led strike group to the Korean Peninsula to press his point, one of a series of measures that indicate his willingness to shake up foreign policy strategy, AFP reported.
"Lately, tensions have risen... and one has the feeling that a conflict could break out at any moment," Chinese Foreign Minister Wang Yi said.
"If a war occurs, the result is a situation in which everybody loses and there can be no winner."
Whichever side provoked a conflict "must assume the historic responsibility and pay the corresponding price," he said.
Wang's comments mirrored a warning from the North Korean Foreign Ministry's Institute for Disarmament and Peace which said "thermo-nuclear war may break out any moment".
"The US introduces into the Korean Peninsula, the world's biggest hotspot, huge nuclear strategic assets... pushing the situation there to the brink of a war," it said according to the North's official news agency KCNA.
Russia on Friday called for "restraint" over the situation in North Korea, warning against any "provocative steps".
"Moscow is watching with great concern the escalation of tensions on the Korean peninsula," Kremlin spokesman Dmitry Peskov told journalists.
"We call for restraint from all countries and warn countries not to pursue actions that could consist of any provocative steps," he added.
Trump has repeatedly said he will prevent Pyongyang from developing a nuclear-tipped ballistic missile capable of reaching the mainland United States.
"We are sending an armada. Very powerful," Trump said Wednesday of the strike group headed by the USS Carl Vinson super carrier.
A White House foreign policy advisor said Friday that the US is assessing military options in response to the North's weapons programs, saying another test was a question of "when" rather than "if."
Pyongyang has responded with defiance, saying it is ready to fight "any mode of war" chosen by the US and even threatening a nuclear strike against American targets.
There are reports of activity at a nuclear test site in North Korea ahead of today's 105th anniversary of the birth of the country's founder Kim Il-sung, which have fueled speculation it could carry out a sixth test.
In the midst of mounting tensions, there has been little sign of strain on the streets of Pyongyang in recent days, where the focus is on preparations for today's anniversary.
North Korean leader Kim Jong-un on Thursday unveiled the sprawling Ryomyong street development, a prestige housing project repeatedly promised in time to mark the occasion.