Shinzo Abe, Japan's Prime Minister, said that the launches "clearly show that North Korea now poses a new level of threat".
The US Strategic Command said its systems detected and tracked the projectile but "determined the missile launch from North Korea did not pose a threat to North America".
North Korea did not say what kind of missiles it had fired, but with a maximum height of 260km, analysts said they were probably medium-range Rodongs or extended-range Scuds.
The KCNA statement said that Kim supervised a rocket launching drill of the Hwasong artillery units, an elite missile division in the Korean People's Army's Strategic Force.
"Respected Supreme Leader Kim Jong Un learned in detail about the preparations for fire strike while going round the ballistic rocket launching grounds," the report said. "At an observation post he was briefed on a launching plan and gave an order to start the drill."
Kim noted that the four missiles, launched simultaneously, "are so accurate that they look like acrobatic flying corps in formation," according to the report.
The 33-year-old marshal also ordered the strategic forces to be on high alert "as required by the grim situation in which an actual war may break out anytime, and get fully ready to promptly move".
The launches coincided with joint US-South Korean military exercises on the southern half of the Korean Peninsula, drills that take place every year and which North Korea views as preparation for an invasion.
Both Abe and South Korea's Prime Minister, Hwang Kyo Ahn, strongly condemned Monday's launches, while China's Foreign Ministry said it "opposes" them.
In New York, a spokesman for the UN Secretary-General António Guterres said he condemned the actions, which "violate Security Council resolutions and seriously undermine regional peace and stability".
In Washington, White House press secretary Sean Spicer said "the Trump Administration is taking steps to enhance our ability to defend against North Korea's ballistic missiles".
"The launches are consistent with North Korea's long history of provocative behavior," he told a press briefing. "The United States stands with our allies in the face of this very serious threat."