Officials said 35 bodies out of 68 have been identified so far as Nepal began a national day of mourning on Monday.

The black box of the Yeti Airlines aircraft has been recovered from the accident site on Monday, as a search is on for the four persons still missing after the plane with 72 people, including five Indians, on board crashed into a river gorge while landing at Nepal's newly-opened airport in the resort city of Pokhara.

Both the cockpit voice recorder and flight data recorder have been recovered as search and rescue teams rappelled down a 300-metre gorge to continue their efforts, which were suspended overnight.

The Cockpit Voice Recorder (CVR) records radio transmissions and other sounds in the cockpit, such as conversations between the pilots, and engine noises. The flight data recorder (FDR) records more than 80 different types of information such as speed, altitude and direction, as well as pilot actions and performance of important systems.

According to Kathmandu airport officials, the boxes were recovered from the site of the accident, a day after Yeti Airlines' 9N-ANC ATR-72 aircraft crashed on the bank of the Seti River between the old airport and the new airport minutes before landing.

The boxes were handed over to the Civil Aviation Authority of Nepal (CAAN), said Sudarshan Bartaula, a spokesperson of the Yeti Airlines.

The boxes could offer vital clues about Sunday's crash - Nepal's deadliest aviation accident in over 30 years.

So far, 68 bodies have been recovered and the search is going on for the remaining four missing persons.

Police Inspector Gyan Bahadur Khadka, acting information officer of the Kaski District Police Office, said that at least 35 bodies have been identified so far.

He said that an autopsy will begin once the process is completed.

The five Indians, all reportedly from Uttar Pradesh, have been identified as Abhisekh Kushwaha, 25, Bishal Sharma, 22, Anil Kumar Rajbhar, 27, Sonu Jaiswal, 35, and Sanjaya Jaiswal.

Of the five Indians, four were planning to participate in paragliding activities in the tourist hub of Pokhara, said a local resident, who travelled with them to Nepal.

A medical team has been airlifted from the Tribhuvan University Teaching Hospital in Kathmandu. As soon as they reach Pokhara, the postmortem will start at Western Regional Hospital in Pokhara, Khadka added.

As the accident site lies in a deep gorge of Seti river, it was very difficult for search operations, the Army sources said.

The plane commanded by Captain Kamal KC, an instructor pilot, made the first contact with the Pokhara control tower from nearly 110 kilometres away.

"The weather was clear. We allocated Runway 30 which is the eastern end. Everything was fine,” Anup Joshi, spokesperson for Pokhara International Airport, was quoted as saying by the Kathmandu Post newspaper.

He added that no problems had been reported.

The flight captain later asked for permission to switch to Runway 12 which is the western end.

"We were not sure why. Permission was granted, and accordingly, the aircraft started its descent,” said Joshi, who is also a senior air traffic controller.

"At 10:32 am, the plane took off from Kathmandu. It was scheduled to land at Pokhara at 10:58 am. Was in continuous contact with Pokhara Tower. The landing clearance of that plane had also been obtained. The weather was also fine. Everything was fine then how the accident happened is a matter of investigation," said Premnath Thakur, General Manager, Tribhuvan International Airport, Kathmandu.

"A high-level investigation team has been formed. Any conclusion can be drawn by checking its voice recorder and other circumstances," Thakur said.

The team will submit its report within 45 days.

Pokhara, the tourist hot-spot lies between two rivers - the Bijayapur and the Seti - which makes it a perfect habitat for birds. Excellent for sightseers, of course, but a terror for pilots.

Flight tracking website FlightRadar24 claimed that the crashed aircraft was 15 years old and equipped with an 'old transponder with unreliable data'.

According to Nepal’s civil aviation body, 914 people have died in air crashes in the country since the first disaster was recorded in August 1955. The tragedy in Pokhara on Sunday is the 104th crash in Nepali skies and the third biggest in terms of casualties.

The only incidents in which more people were killed took place in July and September 1992. Those crashes involved aircraft of Thai Airways and Pakistan International Airlines and left 113 and 167 people dead, respectively.

The last major air accident in Nepal happened on May 29 when all 22 people onboard, including four members of an Indian family, were killed as a Tara Air plane crashed in Nepal's mountainous Mustang district.

Nepal has had a fraught record of aviation accidents, partly due to its sudden weather changes and airstrips located in hard-to-access rocky terrains.