Kim Jong-un executes two senior officials after failed nuclear test.

Kim Jong Un has executed a second official in just five days over a launch delay at North Korea's test missile site.

The unnamed executive allegedly took responsibility for setbacks at the Punggye-ri nuclear base, which led to the date of a rocket launch being pushed back.

Five days ago, a high-ranking official once described as the "second most powerful man in North Korea" disappeared from public life, sparking speculation he may have been executed by death squads.

It is understood the most recent victim was the director of Bureau 131 - a man in charge of building and running the nuclear base.

Reports in the Japanese paper Asahi Shimbun suggest the director has been at the helm since it was formed.

The suspected execution was handed down over a delay to Pyongyang's sixth missile test and the subsequent collapse of tunnels, which killed 200 workers.

A source told the paper: "It seems he took the blame as the prolonged mining of the nuclear facility pushed back the test date to September when it was initially set for spring."

Last month, Seoul warned that one more North Korean nuclear detonation could destroy its mountain test site and trigger a radiation leak.

South Korea says any future nuclear test by Kim Jong Un risks collapsing the location set aside for launching missiles.

Seoul detected several earthquakes near the hermit nation's nuclear test site in the country's northeast after its sixth and most powerful bomb explosion in September.

The unnamed executive allegedly took responsibility for setbacks at the Punggye-ri nuclear base (pictured) which led to the date of a rocket launch being pushed back. Photo / 39 North

Experts say the quakes suggest the area is now too unstable to conduct more tests there.

US experts issued a similar warning, stating a second nuclear test site in North Korea's northwest could cave in but that it won't be abandoned.

Five of Pyongyang's recent tests have been carried out under Mt Mantap at the Punggye-ri military base in the northwest of North Korea.

But now the base is said to be suffering from "Tired Mountain Syndrome" after three small earthquakes occurred nearby after the blasts.

Last week, speculation was rife of the execution of General Hwang Pyong-so, who was once the most senior military official in the hermit state as a Vice-Marshall after the supreme leader.

It came days after Kim Jong Un visited the significant Mt Paektu, a sign that suggested he was planning to execute a top official.

Such visits to the mystical mountain often precede important decisions by North Korean leaders.

Pyong So was reported to have been expelled from the party for "taking bribes" and has not been seen since October.

His deputy Kim Wong Hong is said to have been banished to a prison camp.

The South Korean JoongAng Ilbo reported: "If Hwang was indeed kicked out of the Workers' Party, it would practically mean the end of his political career, and possibly his life, though it is unknown whether or not he is still alive."

"Kim visited the mountain and ordered the site managers to construct hospitable accommodations on the mountain for visitors," the state-run KCNA reported.

In November 2013, the despot visited the mountain with his aides a month before he executed top officials including Jang Song Thaek, his uncle and political guardian.

Kim visited the mountain again in April 2015, before executing Hyon Yong Chol, a former defence chief.

He had also made a pilgrimage after North Korea's fifth nuclear test in September 2016.

Pictures show Kim wandering around on the snow-capped mountain with hardly a bead of sweat and wearing spotless and shiny shoes.

NzHerald.