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.
Image from North Korean TV of rocket launch on 7 February 2016Image copyrightReuters
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North Korean TV broadcast the launch of the rocket
Kim Jong-un signs document regarding rocket launch, on 7 February 2016Image copyrightReuters
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Kim Jong-un is shown signing-off on the rocket launch
A flying object soars into the air above North Korean territory as seen from the Chinese border city of Dandong, 7 FebruaryImage copyrightReuters
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An object which appeared to be a rocket was spotted above North Korean territory from the Chinese border city of Dandong
Picture from North Korean TV of the rocket after launch, on 7 February 2016Image copyrightAFP
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An image from the rocket is broadcast on Korean TV
North Koreans watch announcement of launch in Pyongyang on 7 February 2016Image copyrightAP
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North Koreans watched the launch announcement on a big screen in the capital Pyongyang
'Fascinating vapour'
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).
The rocket 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".