US President Barack Obama urged Pyongyang to "refrain from further provocative actions".
"North Korea broke the rules once more by testing a rocket that could be used for a long-range missile," Mr Obama told a crowd in the Czech capital, Prague.
Obama condemns North Korea launch
"This provocation underscores the need for action - not just this afternoon at the UN Security Council, but in our determination to prevent the spread of these weapons."
Later a joint US-EU statement urged Pyongyang to abandon its pursuit of weapons of mass destruction and "policy of threats aimed at its neighbours".
The launch "harms peace and stability in northeast Asia", the statement added.
The Security Council approved a Japanese request for the emergency session.
Washington, Tokyo and Seoul regard the launch as a clear violation of Security Council resolution 1718 adopted in October 2006, which bans North Korea from carrying out ballistic missile activity.
However, both China and Russia have urged restraint in the international response.
'No threat to US'
In a statement on its website, the US Northern Command said North Korea launched a three-stage Taepodong-2 missile at 0230 GMT.
"Stage one of the missile fell into the Sea of Japan/East Sea. The remaining stages along with the payload itself landed in the Pacific Ocean.
"No object entered orbit and no debris fell on Japan."
US military authorities "assessed the space launch vehicle as not a threat to North America or Hawaii and took no action in response to this launch", the statement added.
Earlier, state media in North Korea said that the "Kwangmyongsong-2" satellite had been placed in orbit.
The satellite was transmitting data and the "Song of General Kim Il-sung" and "Song of General Kim Jong-il" - references to the late founder of North Korea and his son, the current leader - the report said.
The BBC's John Sudworth in Seoul says a failure would seriously detract from North Korea's ability to exploit the propaganda value of the launch, although it may never admit it to its own people.
In a previous satellite launch attempt in 1998, North Korea said it was sending up a device that would orbit the world transmitting revolutionary melodies.
It claimed this was also successful but the launch is believed to have been a failure as no trace of the satellite was ever found.
Testing technology?
North Korea gave prior warning of the launch and repeatedly said it was using it as part of the peaceful pursuit of a space programme, as is its right under international law.
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