North Korea launched a long-range rocket on Wednesday, in defiance of UN sanctions threats over what Pyongyang's critics insist is a disguised ballistic missile test.
"It (the rocket) has been launched," a South Korean defense ministry spokesman said without elaborating further.
The Yonhap news agency, citing a government source, said the rocket had taken off from the Sohae satellite launch center at 9:51 am and was immediately detected by navy vessels deployed by Seoul in the Yellow Sea.
There was no immediate report on the success of the launch, but the Japanese government said the missile had passed its southern island chain of Okinawa around 12 minutes after take-off.
"The missile that North Korea calls a satellite passed over Okinawa around 10:01 (am). We launched no interception," it said.
Japan had deployed missile defense systems to intercept and destroy the rocket if it looked set to fall on its territory.
The United States had also deployed ships from its Pacific fleet equipped with ballistic missile defenses.
Yonhap said the three-stage rocket's first stage had separated as scheduled and splashed down in the sea off South Korea's southwest coast.
In Seoul, President Lee Myung-Bak called an emergency meeting of his National Security Council to discuss the implications of the launch.
Japan's government found the launch intolerable, chief government spokesman Osamu Fujimura said.
"It is extremely regrettable that North Korea went through with the launch despite our calls to exercise restraint," he said.
The launch followed reports in the South Korean media and satellite imagery analysis by US experts that suggested the rocket had been removed from the launch pad to repair an apparent technical problem.
North Korea had originally provided a December 10-22 launch window, but extended that by a week on Monday when a "technical deficiency" was discovered in the first-stage control engine.
North Korea last attempted to launch its three-stage Unha-3 carrier in April, but the rocket exploded shortly after take-off.
A successful launch this time would carry profound security implications, marking a major advance in the North's bid to mate an intercontinental ballistic missile (ICBM) capability with its nuclear weapons program.
Washington and its allies insist the launch is a disguised ballistic missile test that violates UN resolutions triggered by Pyongyang's two nuclear tests in 2006 and 2009.