North Korea says it has successfully tested an intercontinental ballistic missile capable of "striking the whole US mainland".
Pyongyang claimed the missile, known as Hwasong-15, is nuclear-capable and the most powerful weapon it has ever tested.
In a broadcast on state television, the isolated state said the new ICBM was "significantly more" powerful than the previous two long-range weapons it tested, and is capable of carrying a "super-large heavy warhead".
US Defence Secretary James Mattis described the test as a step toward missiles that can "threaten everywhere in the world", while President Donald Trump said "we will take care of it" when questioned about the launch.
The missile flew 590 miles (950km) to an altitude of 2,781 miles (4,475km) for 53 minutes – more than 10 times the height of the International Space Station.
North Korea said its nuclear weapons pose no threat to any country as long as its own interests are not infringed upon.
In an address by veteran newsreader Ri Chun Hee, Pyongyang added the missile was developed to "defend the sovereignty and territorial integrity of the country from the US imperialists' nuclear blackmail policy and nuclear threat".
The launch was detected early on Wednesday morning local time from a site near the North Korean capital, hours after Mr Kim was pictured touring a catfish factory.
The ICBM appeared to have been launched from Pyongsong, according to South Korea's joint chiefs of staff, over the sea between South Korea and Japan.
A US government source confirmed the launch and the Pentagon said there was no threat to the US or its allies.
An unnamed South Korean lawmaker told Seoul's Yonhap news agency the South's intelligence agency had not ruled out another nuclear test by the North.
Japan's defence minister Itsunori Onodera said the missile broke up before it landed in the sea, inside the country's exclusive economic zone.
South Korea immediately reacted to the test by launching three missiles in a show of force.
The South's president, Moon Jae-in, said he was worried the growing threat could force the US to attack the North.
"If North Korea completes a ballistic missile that could reach from one continent to another, the situation can spiral out of control," Moon said at an emergency meeting in Seoul.
"We must stop a situation where North Korea miscalculates and threatens us with nuclear weapons or where the United States considers a pre-emptive strike."
Mr Moon and Mr Trump held a phone conversation hours after the missile launch.
"The two leaders strongly condemned North Korea for again launching a long-range ballistic missile despite the international community's repeated warnings and its continued sanctions and pressure under a series of UN Security Council resolutions," a spokesman for Mr Moon said.
He added: "The two leaders agreed to continue their efforts to bring North Korea to the dialogue table by continuing to put sanctions and pressure on North Korea in close cooperation with the international community."
The UN Security Council is meeting later to discuss the missile test following requests from the US and Japan.