A Russian Antonov An-24 passenger plane carrying 48 people crashed in the country's far east on Thursday as it was preparing to land, killing everyone on board, the regional governor and investigators said.

The burning fuselage of the plane, which was made in the Soviet era and was nearly 50 years old, was spotted on the ground by a helicopter.

There were 42 passengers, including five children, and six crew members on board.

Investigators said they had opened a criminal case into the suspected violation of air traffic and air transport rules, resulting in the death of more than two people through negligence.

Video shot from a helicopter showed the plane came down in a densely forested area and pale smoke could be seen rising from the crash site. There were no roads to the site and a rescue team numbering over 100 people had to use heavy machinery to cut a path there.

Vasily Orlov, the regional governor, offered his condolences to the families of those who died and declared three days of mourning, ordering flags to be lowered to half mast.

"I regret to inform you that, according to preliminary data, there are no survivors of the An-24 plane crash in the Tynda District. Rescuers have reached the crash site," he said in a statement.

The plane was on a flight by a privately owned Siberian-based regional airline called Angara. The aircraft's tail number showed it was built in 1976 and was operated by Soviet flag carrier Aeroflot before the 1991 collapse of the Soviet Union.

It was en route from the city of Blagoveshchensk to Tynda, a remote town and important railway junction in the Amur region bordering China, and dropped off radar screens while preparing to land.

Debris from the plane was found on a hill around 15 km (10 miles) from Tynda, the Interfax news agency quoted emergency service officials as saying.

A representative from Angara told Reuters they could not offer any more details.

The federal Russian government said it had set up a commission to deal with the aftermath of the crash and authorities announced an investigation into the cause.

The Kremlin said President Vladimir Putin had been notified of the crash.

At least one Chinese citizen was reported to have been on board and Chinese President Xi Jinping sent his condolences to Putin over the crash.

'FLYING TRACTORS'

Angara airline is based in the Siberian city of Irkutsk and serves airports in Siberia and Russia's far east. It operates 10 An-24s built between 1972 and 1976, according to the RussianPlanes web-portal.

It was one of two Siberian airlines that last year asked the Russian government, opens new tab to extend the service life of the Antonov aircraft, as Russian planemakers scramble to plug the gap left by an exodus of foreign manufacturers.

Nicknamed "flying tractors" by some, the propeller-driven An-24s are regarded as reliable workhorses by the Russian aviation industry and are well-suited to the harsh conditions in Siberia as they are able to operate in sub-zero conditions and don't have to land on runways.

But airline executives, pilots and industry experts say the cost of maintaining the Antonovs - which make up a fraction of Russia's fleet of over 1,000 passenger planes - has increased after Western sanctions against Russia over its war in Ukraine hit investment and access to parts.

Many of the planes were due to be retired from service in the coming years, but mass production of the new Ladoga aircraft, the same class as the An-24, is not due to begin until 2027 at the earliest.