Kazakhstan on Wednesday mourned the deaths of 27 people in one of its worst ever aviation disasters, a tragedy that wiped out much of the top echelon of the state border service including the acting chief.

The KNB state security service confirmed that all 27 crew and servicemen on board the An-72 military jet were killed Tuesday evening when it crashed close to Shymkent airport in the south of the country.

"All 27 occupants of the aircraft, including seven crew members, have perished," the National Security Service (KNB) said in a statement.

The victims included the acting head of the Kazakh federal border service Turganbek Stambekov and his wife, the statement said.

The disaster also claimed the lives of much of the top leadership of the border service, with a total of 11 top officials killed.

Another five lieutenant-colonels from the regional Ontustik border unit were killed as well as three rank-and-file servicemen.

President Nursultan Nazarbayev declared December 27 a day of national mourning and expressed his "deepest condolences to the families and loved ones of the dead", the presidency said.

He said it appeared that there was no indication of foul play and the disaster appeared to be the result of an "accumulation of tragic circumstances" including bad weather.

KNB chief Nurtai Abykayev told reporters in Shymkent that the causes of the disaster could have been "the weather conditions, the human factor and the technical condition of the aircraft."

The black box of the plane has been found, he added, quoted by the Interfax-Kazakhstan news agency.

The KNB said the passengers had been attending a meeting of border guards in the capital Astana and were on their way to an end-of-year security meeting in Shymkent.

The 22-year-old plane crashed about 20 kilometres (12 miles) from Shymkent airport where it had been due to land after a flight from Astana.

Kazakhstan's KTK television said the jet fell from a height of 800 metres (2,600 feet). Witnesses also reported hearing a loud explosion at the time of the crash.

Footage of the crash site aired on Kazakh state television showed only fragments of the An-72 plane remaining on the ground.

But the KNB stressed that the plane had recently undergone all the necessary checks and repairs.

Khabar state television also cited local residents as saying that a heavy winter storm had descended on the region at the time of the accident. It said the plane caught fire after the crash.

The border guard service of Kazakhstan -- a vast resource-rich nation nestled between China and Russia -- had already experienced tragedy this year.

Its acting head Stambekov was appointed to his post in June after his predecessor was fired following a May incident in which 14 border guards were shot dead in a remote outpost in the south of the country.

The sole border guard to survive the shooting confessed during a subsequent trial that he killed his colleagues, but retracted his confession after being handed a life sentence, saying unidentified people in civilian clothes were responsible.

But Abykayev warned people against making any link between the two tragedies.

"I see no connection. People are recalling what happened to the border guards. I regret that people are thinking this way. We are experiencing great grief -- there is no need to mix things up."

Aviation disasters remain a scourge across the former Soviet Union due to ageing hardware that often has not been replaced since the fall of the Soviet regime, as well as human error.

In November, eight people were killed in Kazakhstan when a Russian-made Mi-8 helicopter crashed while on a pipeline surveillance mission.