Seoul Said on Friday that Pyongyang would stage a third nuclear test, as Hundreds of thousands of North Koreans celebrated the country’s rocket launch.

Seoul Said on Friday that Pyongyang would stage a third nuclear test, as Hundreds of thousands of North Koreans celebrated the country's rocket launch.

"A nuclear test is highly probable, and judging from analysis of intelligence, significant preparations have been made," a top South Korean official said.

"North Korea has a track record of conducting nuclear tests following missile launches whose aim was to develop a delivery system for nuclear warheads," Unification Minister Yu Woo-Ik told a parliamentary committee, without elaborating.

The South’s claim comes two days after North Korea fired a long-range rocket on Wednesday.

Also on Friday, hundreds of thousands of North Koreans rallied in the freezing cold to celebrate the country's rocket launch, staging a choreographed show of defiance under their youthful leader's "endless" wisdom.

The enormous rally in central Pyongyang, shown on state television, came two days after the launch of the three-stage rocket and just ahead of the anniversary Monday of the death of new leader Kim Jong-Un's father.

Unbowed, North Korean state media said Kim, who is in his late 20s, had personally signed off on the rocket launch and had declared his regime's "unshakable stand" that the program will continue.

Kim stressed the need "to launch satellites in the future... to develop the country's science, technology and economy", according to the North's official Korean Central News Agency (KCNA) as it gave new details of the launch.

The "dear respected Marshal" visited mission control an hour before the rocket took off on Wednesday morning and praised the "ardent loyalty and patriotic devotion" of the technical team, KCNA said in the report early Friday.