North Korea has fired a long-range rocket carrying what it calls a satellite but critics claim Pyongyang is testing missile technology in defiance of UN sanctions.
The controversial launch comes just weeks after a nuclear bomb test.
The US Strategic Command said on Sunday it had detected a missile entering space and South Korea's military said the rocket had put an object into orbit.
North Korea said the launch of the satellite Kwangmyongsong-4, named after late leader Kim Jong Il, was a "complete success" and making a polar orbit of Earth every 94 minutes.
The launch order was given by his son, leader Kim Jong Un, who is believed to be 33 years old.
The launch prompted South Korea to announce it would begin talks with the United States on the deployment of an advanced missile defence, which China and Russia both oppose, to counter what South Korea sees as the North's threat.
North Korea's state news agency carried a still picture of a white rocket that closely resembled a previously launched rocket, lifting off.
Another showed Kim surrounded by cheering military officials at what appeared to be a command centre.
North Korea's last long-range rocket launch, in 2012, put what it called a communications satellite into orbit but no signal has ever been detected from it.
"If it can communicate with the Kwangmyongsong-4, North Korea will learn about operating a satellite in space," said David Wright, co-director and senior scientist at the Global Security Program of the Union of Concerned Scientists.
"Even if not, it gained experience with launching and learned more about the reliability of its rocket systems."
The rocket lifted off about 9.30am Seoul time on a southward trajectory, as planned.
Japan's Fuji Television Network showed a streak of light heading into the sky, taken from a camera at China's border with North Korea.
North Korea had notified UN agencies it planned to launch a rocket carrying an Earth observation satellite, triggering opposition from governments that see it as a long-range missile test.
The UN Security Council was scheduled to hold an emergency meeting on Sunday to discuss the launch, at the request of the United States, Japan and South Korea, diplomats said.
Isolated North Korea had initially given a February 8-25 time frame for the launch but on Saturday changed that to February 7-14, apparently taking advantage of clear weather.
North Korea's National Aerospace Development Administration called the launch "an epochal event in developing the country's science, technology, economy and defence capability by legitimately exercising the right to use space for independent and peaceful purposes".
The launch and the January 6 nuclear test are seen as efforts by the North's young leader to bolster his domestic legitimacy ahead of a ruling party congress in May.
South Korea said it would begin discussions with the United States on an advanced missile-defence system called Terminal High Altitude Area Defence, adding that it would only be used to target the North.
Its military said it would make annual military exercises with US forces "the most cutting-edge and the biggest" this year.
US Secretary of State John Kerry said the United States would work with the UN Security Council on "significant measures" to hold North Korea to account for what he called a flagrant violation of UN resolutions on North Korea's use of ballistic missile technology.
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