Kim Jong-un's rockets are capable of reaching America but would not work when they got there, according to analysts.

The North Korean dictator carried out a test launch of his Hwasong-14 intercontinental ballistic missile in the north of the country on Friday.

US and South Korean experts have analysed Japanese footage capturing the rocket's re-entry vehicle shortly before it crashed into the sea.

They said the video suggests it failed to survive the extreme heat and pressure after re-entering the Earth's atmosphere following its launch.

But the apparent failure likely means the North will conduct more flight tests of the Hwasong-14 missile to ensure the warhead could survive the re-entry from space and hit its intended target, the analysts said.

North Korean dictator Kim Jong-un carried out a test launch of his Hwasong-14 intercontinental ballistic missile in the north of the country on Friday

Kim Jong-un's rockets are capable of reaching America but would not work when they got there, according to analysts

The Hwasong-14 ICBM, which was first tested on July 4, follows decades of effort by North Korea to obtain a nuclear deterrent against the United States.

Analysis of the flight data from Hwasong-14's second test has suggested that more of the U.S. mainland, including Los Angeles and Chicago, is now in range of Pyongyang's weapons.

However, whether North Korea can arm the missile with a nuclear warhead and protect it throughout the flight are different questions entirely.

After analyzing video from a rooftop camera operated by Japan's NHK television on the northern island of Hokkaido, U.S. missile expert Michael Elleman concluded that Hwasong-14's re-entry vehicle 'disintegrated' before it landed at sea.

In an article posted at the 38 North website, Elleman said the video showed the re-entry vehicle shedding small radiant objects at an altitude of 2.5 to 3 miles.

He said the re-entry vehicle dims and quickly disappears at an altitude of 1.9 to 2.5 miles before it passes behind a mountain range and is obscured from the camera's view.

A man walks in front of a public TV screen broadcasting news of North Korea's test-firing of its second intercontinental ballistic missile, in Tokyo, Japan

Had the re-entry vehicle survived, it would have continued to glow until disappearing behind the mountains, Elleman said.

'In short, a reasonable conclusion based on the video evidence is that the Hwasong-14's re-entry vehicle did not survive during its second test,' said Elleman, an expert with the International Institute for Strategic Studies.

'If this assessment accurately reflects reality, North Korea's engineers have yet to master re-entry technologies and more work remains before Kim Jong Un has an ICBM capable of striking the American mainland.'

Granted, it's impossible to know how the warhead would have performed if North Korea had launched the missile for real.

Both ICBMs were test-launched at highly lofted angles to reduce the range and avoid neighboring countries, and the near-vertical flight paths meant the re-entry vehicles endured harsher conditions during their descents.

But Kim Dong-yub, a defense analyst at the Institute for Far Eastern Studies at Kyungnam University in Seoul, said it's obvious North Korea has yet to reach where it wants to be with re-entry technologies.

While North Korea has declared that the Hwasong-14's latest launch confirmed important features of the missile, such as its range and the warhead's atmospheric re-entry, it also described the rocket as 'landing in the target waters in the open sea.'

That probably wasn't an ideal outcome for North Korean engineers because nuclear warheads are usually designed to detonate at lower altitudes shortly before impact, Kim said.

'Considering the cost and efforts they put into tests, North Korea likely would have tried to detonate the warhead properly; they apparently failed this time, but could focus on this aspect in future tests,' Kim said.

Mastering warhead re-entries would be one of the most critical military milestones the North has left, along with developing a submarine-launched ballistic missile system and solid-fuel ICBMs, Kim said.