"North Korea launched a long-range rocket at 07:39 am (2239 GMT Thursday)," a South Korean defence ministry spokesman told AFP.
"US and South Korean intelligence authorities are seeking to determine whether it was a successful launch," he said.
Yonhap news agency also quoted a government source as saying that South Korea was tracking the rocket`s trajectory.
Japananese authorities said that the North Korean `flying object` had fallen into the ocean.
Immediately after the launch, South Korea issued an order urging residents near the inter-Korean border to seek shelter to protect themselves from any debris that might fall from the rocket, Yonhap said.
North Korea has previously said the rocket will place a satellite in orbit for peaceful research purposes, but Western critics see the launch as a thinly veiled ballistic missile test, banned by United Nations resolutions. (*)