South Korea's navy has launched a salvage operation to retrieve the debris from North Korea's failed rocket launch, a military spokesman said.
North Korea has admitted its launch of a long-range rocket failed after it broke up and fell into the Yellow Sea.
The failure of the supposed Unha-3 rocket, which the US says was actually a long-range ballistic Taepodong-2 missile, is a major setback for the North's regime.
The launch has attracted international condemnation and the UN Security Council will hold an emergency meeting later Friday.
In a broadcast on state TV, North Korea said its scientists were trying to determine why the rocket failed.
It exploded just minutes after launch, with pieces of it falling into the Yellow Sea west of the South Korean capital Seoul.
South Korea's announcement of the salvage operation came despite a warning from the North last week for it not to attempt such an operation.
"If anyone... attempts to shoot down or to salvage our space rocket debris, we would retaliate ruthlessly," Pyongyang's Committee for the Peaceful Reunification of the Fatherland, in charge of inter-Korean ties, had said.
Yonhap news agency said more than a dozen South Korean ships, many of them equipped with sonar and backed by divers, were combing the area.
"We believe some large chunks are lying on the sea bed," the spokesman said.
The depth of the sea is between 70 and 100 metres, making it feasible to retrieve large chunks of debris, Yonhap reported.