North Korea has fired a long-range rocket, which critics say is a test of banned missile technology.
A state TV announcer said that North Korea had successfully placed a satellite in orbit.
The launch was condemned by Japan, South Korea and the US, who have requested an emergency meeting of the UN Security Council later on Sunday.
South Korea says it is to begin discussing with the US the deployment of a missile defence system.
Senior defence official Ryu Je-Seung said if the THAAD missile system – considered one of the most advanced in the world – were deployed it would be only to counter the threat from the North.
In a statement, the North Korean National Aerospace Development Administration said earth observation satellite Kwangmyongsong-4 had entered orbit about 10 minutes after lift-off from the Sohae space centre in North Phyongan province.
Announcing the launch on state TV, a newsreader said it had been ordered by North Korea’s leader Kim Jong-un and said the country planned to launch more satellites in the future.
“The fascinating vapour of Juche satellite trailing in the clear and blue sky in spring of February on the threshold of the Day of the Shining Star,” was how the launch was described.
South Korean Defence Ministry spokesman Moon Sang Gyun said a warship had detected the launch at 09:31 (00:31 GMT).
South Korean MPs were told in a behind-closed-doors briefing by the country’s spy agency later on Sunday that the launch should be treated as a ballistic missile test as the satellite it put into orbit would be useless.
The payload was presumed to weigh 200kg (440lbs), double the size of the one launched in 2012, but much lighter than the 800-1,500kg usual for a satellite.
They were also reportedly told North Korea has the technology for inter-continental ballistic missiles and is preparing a fifth nuclear test, South Korean news agency Yonhap reported.
The launch was roundly condemned by the international community. US Secretary of State John Kerry called it a “flagrant violation” of UN resolutions and warned of “significant measures to hold the DPRK [North Korea] to account.”
China said it “regrets” North Korea’s actions but urged “the relevant parties” to “refrain from taking actions that may further escalate tensions on the Korean peninsula“.