SEOUL: One of the stages of North Korea's satellite launch rocket exploded after separation on Tuesday (Nov 21), video captured by a South Korean astronomy observatory showed, in what some analysts said may have been deliberate destruction to prevent recovery.

North Korea launched its first spy satellite into orbit on Tuesday, after two previous attempts this year ended with the rockets crashing during flight.

The video was filmed by a camera that South Korea's Yonsei University uses for watching meteors. Analysts said it showed the Chollima-1 rocket crossing the sky, and a stage separating. The lower stage then falls away for a few moments before erupting in a flash and cloud of debris.

"This time they appear to have detonated the first stage propellant in mid-air," Byun Yong-Ik, an astronomy professor at Yonsei University, told Reuters.

"This kind of measure was not seen in the previous launch attempts, and it could have been an effort to prevent South Korean and US authorities from recovering the propellant as it is equipped with a new engine."

Marco Langbroek, a satellite expert at Delft University of Technology in the Netherlands, said the video showed the first and second stage, with the first stage blowing up after separation of the second stage.

"This certainly is unusual," he told Reuters, noting that most rocket stages are left to fall into the sea.

It's not possible to tell for sure if it was intentional or an accident, but North Korea said it had used a self-destruct mechanism during its last launch in August as a safety measure after the rocket failed, Langbroek said.

"I feel it is certainly possible that it was done intentionally, to prevent recovery of an intact stage by the West," he said.

The South Korean military is seeking to find and salvage debris from the rocket, South Korea's defence ministry told parliament on Thursday.

The ministry said it had no comment on the video or reports of deliberate destruction.

After the first Chollima-1 launch in May plunged into the sea between the Korean peninsula and China, the South Korean and US navies recovered parts of the rocket, including its satellite payload, which they said "was not suitable for military use".

Recovering parts of the rocket could provide valuable intelligence on its capabilities and components, experts have said, and South Korea has accused Russia of providing technical aid to North Korea for this latest launch.

Russia denied any military cooperation, but President Vladimir Putin in September publicly promised to help North Korea build satellites.

North Korean rocket stage exploded after satellite launch, video shows