North Korea said it has successfully tested an intercontinental ballistic missile capable of "striking the whole US mainland".
Pyongyang claimed the nuclear-capable missile, known as Hwasong-15, is the most powerful weapon it has ever tested.
In a broadcast on state television, the isolated state added that the new ICBM was "significantly more" powerful than the previous two long-range weapons it tested, and it is capable of carrying a "super-large heavy warhead".
Kim Jong Un added that Hwasong-15 "met the goal of its missile development".
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.
Ri Chun Hee, the veteran newsreader who is relied upon to deliver major announcements, said: "The development and advancement of the strategic weapon of the Democratic People's Republic of Korea (DPRK) are to defend the sovereignty and territorial integrity of the country from the US imperialists' nuclear blackmail policy and nuclear threat, and to ensure the peaceful life of the people, and therefore, they would not pose any threat to any country and region as long as the interests of the DPRK are not infringed upon."
The launch was detected after it was fired early on Wednesday morning local time from a site near the capital city.
The ICBM appears to have been launched from Pyongsong, according to South Korea's joint chiefs of staff, over the sea between South Korea and Japan.
Mr Kim was pictured just hours before the announcement touring a catfish factory.
"We will take care of it"
Following the test, President Donald Trump said "we will take care of it" when questioned about the missile launch.
A US government source confirmed the launch and the Pentagon has said there is no threat to the US or its allies.
An unnamed South Korean lawmaker told Yonhap that the South's intelligence agency has 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.
The launch comes after 75 days of no activity from the North following an intermediate range missile flying over Japan on 15 September.
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 is 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," Seoul's presidential office spokesman Park Soo-hyun told a press briefing.
"Also, 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, while firmly and strongly dealing with North Korean provocations based on the strong joint defense posture of South Korea and the United States," he added.
The UN Security Council will meet at 3pm (8pm Irish time) on Wednesday after requests from the US and Japan to discuss the missile firing.
