(BSS/AFP) - North Korean leader Kim Jong Un has fired his vice premier and railed against "incompetent" officials in a rare and very public broadside against apparatchiks at the opening of a critical factory, state media said Tuesday.

Vice Premier Yang Sung Ho was sacked "on the spot", the state-run Korean Central News Agency (KCNA) said, in a speech in which Kim attacked "irresponsible, rude and incompetent leading officials".

"Please, Comrade Vice Premier, resign by yourself when you can do it on your own before it is too late," Kim reportedly said.

Nuclear-armed North Korea, which is under multiple sets of sanctions over its weapons programmes, has long struggled with its moribund state-managed economy and chronic food shortages.

Kim has been quick to scold lazy officials for alleged mismanagement of economic policy but such a public dismissal is very rare.

Touring the opening of an industrial machinery complex on Monday, Kim blasted cadres who for "too long been accustomed to defeatism, irresponsibility and passiveness".

Yang was "unfit to be entrusted with heavy duties", Kim said, according to KCNA.

"Put simply, it was like hitching a cart to a goat -- an accidental mistake in our cadre appointment process," the North Korean leader explained.

"After all, it is an ox that pulls a cart, not a goat."

And he urged a quick turnaround in the "centuries-old backwardness of the economy and build a modernized and advanced one capable of firmly guaranteeing the future of our state".

Images released by Pyongyang showed a stern-looking Kim delivering a speech at the venue in Hamgyong Province in the country`s frigid northeast, with workers in attendance wearing green uniforms and matching grey hats.

- Lazy officials -

The impoverished North has long prioritised its military and banned nuclear weapons programmes over providing for its people.

It is highly vulnerable to natural disasters including flood and drought due to a chronic lack of infrastructure, deforestation and decades of state mismanagement.

The new machine complex makes up part of a large machinery-manufacturing belt linking the northeast to Wonsan further south, "accounting for about 16 percent of North Korea`s total machinery output", according to Yang Moo-jin of the University of North Korean Studies.

Kim`s public dismissal of Yang mirrors past cases such as Jang Song Thaek, Kim`s uncle, who was executed in 2013 after being accused of plotting to overthrow his nephew, Yang said.

The North Korean leader is "using public accountability as a shock tactic to warn party officials", he told AFP.

Pyongyang is gearing up for its first congress of its ruling party in five years, with analysts expecting it in the coming weeks.

Economic policy, as well as defence and military planning, are likely to be high on the agenda.

Last month, Kim vowed to root out "evil" at a major meeting of Pyongyang`s top brass.

State media did not offer specifics, though it did say the ruling party had revealed numerous recent "deviations" in discipline -- a euphemism for corruption.