Both the US State Department and the Japanese government have issued stark statements condemning the blast-off.
Japan said the launch was "regrettable" and the US called it "provocative" and said "appropriate steps" would be taken.
"We have had a launch. I don't know the type of missile," said US State Department spokesman Fred Lash.
Japanese broadcaster NHK said there were no reports of any debris falling on Japan.
It appears that wreckage from the rocket fell in the Pacific Ocean.
International pressure had mounted in recent days to halt the launch at Musudan-ri on the north-east coast.
North Korea had said its intentions were peaceful and it was launching an "experimental communications satellite".
But the US and North Korea's neighbours believe it is a cover for testing the regime's long-range missile technology in defiance of UN resolutions.
The long-range rocket is capable of hitting the US.
Before the blast-off, North Korean leader Kim Jong-il appeared to make a rare public appearance, when he visited a theatre in Pyongyang.
President Obama had warned that the international community would take action if North Korea went ahead with the launch.
"We will work with all interested partners in the international community to take appropriate steps to let North Korea know that they cannot threaten the safety and stability of other countries with impunity," he said.
North Korea said it had the right to launch the rocket as part of a peaceful space programme.
But the US views it as a violation of a UN Security Council resolution passed after Pyongyang's nuclear and missile tests in 2006.
Click to view image: 'ffcb2693f7fe-15253561.jpg'
|Liveleak on Facebook|