All 48 people aboard a Russian passenger plane that vanished from radar in the Far East have died, authorities confirmed Thursday, after the aircraft’s wreckage was found on a remote mountainside.

The Antonov An-24 was en route from the regional capital of Blagoveshchensk to the town of Tynda when it disappeared earlier in the day. The Russian Emergency Situations Ministry later reported that the wreckage was discovered about 16 kilometers (10 miles) from Tynda, near a rugged section of mountainous terrain.

Amur regional Governor Vasily Orlov said the aircraft had been carrying 43 passengers — including five children — and six crew members.

“This terrible tragedy took the lives of 48 people,” he wrote in a Telegram post, declaring three days of mourning across the region, which borders China’s northeastern Heilongjiang province.

The aircraft, a twin-propeller Antonov-24 operated by Angara Airlines, was headed to the town of Tynda from the city of Blagoveshchensk when it disappeared from radar at around 1:00 pm local time (0400 GMT).

A rescue helicopter later spotted the burning fuselage of the plane on a forested mountain slope about 16 kilometres (10 miles) from Tynda.

Although local rescuers said the forest terrain made it difficult to get to the crash site, the Amur region’s civil defence agency said it was dispatching a ground team to the scene.

“At the moment, 25 people and five units of equipment have been dispatched, and four aircraft with crews are on standby,” the agency told local reporters. They further explained that main search operations are being conducted by air.

According to Russia’s Far Eastern Transport Prosecutor’s Office, the plane crashed while attempting a second approach to Tynda airport. While approaching Tynda Airport, the aircraft went around for a second landing, after which contact was lost.

“The circumstances are being investigated,” the Transport Prosecutor’s office said to Russia’s TASS news agency.