North Korea has released video footage of a purportedly new submarine-launched ballistic missile (SLBM) test, three days after it claimed it had successfully tested its first hydrogen bomb.

But South Korean media suggested the footage broadcast by state Korean Central TV late Friday was an edited compilation of the North's third SLBM test, conducted last month in the Sea of Japan, and a different ballistic missile test from 2014.

The undated footage shows leader Kim Jong-Un, on board a military vessel in a winter coat and a fedora hat, looking on as a missile is launched vertically from underwater and ignites in mid air.

The video then cuts to a rocket flying through the clouds, suggesting the missile was able to reach such altitudes.

But South Korean media said the images of a rocket rising through the clouds was in fact taken from footage of a SCUD missile test broadcast in 2014.

North Korea first announced in May that it had conducted a successful SLBM test, a claim accompanied by pictures of Kim pointing at the missile as it blasted out of the water at a 45-degree angle.

A second SLBM test was carried out off the southeastern port of Wonsan in November but this was apparently a failure as only debris from its casing was seen in the sea and no traces of the flight were detected.

South Korean military officials say the North is continuing to actively pursue the development of SLBMs, which would take its nuclear threat to a new level.