Algerian search teams recovered one of the black box flight recorders of a military plane on Wednesday in their quest for clues to why it crashed killing all but one of 78 people on board.

Algerians began three days of mourning for the dead from the crash of the C-130 Hercules transport aircraft in the mountainous Oum El Bouaghi region of the northeast on Tuesday -- the country's worst air disaster in a decade.

Officials said one seriously injured survivor was found in the wreckage.

The remainder of the 74 passengers and four crew were all killed when the plane came down in bad weather.

A source close to the specialist search teams said they had located the black box flight recorder, which was in "good condition," the national APS news agency reported.

The plane had plummeted "nose first" before hitting the ground, the source said, adding that it would have been contending with strong winds and poor visibility.

Emergency services chief Mustapha Lahbiri said search teams had been scouring the snowy and rugged area with sniffer dogs since early morning.

The male survivor, who was in a "critical" condition after suffering serious head injuries, was being treated in a military hospital in the city of Constantine, east of the capital, where the plane had been headed.

Bereaved families arrived at the same Constantine hospital throughout the day to collect their loved ones' remains.

Among the dead were the wife and daughter of a senior military officer, the defence ministry said.

The plane was flying from the desert garrison town of Tamanrasset in the deep south to Constantine, 320 kilometres (200 miles) east of Algiers, and lost contact with the control tower as it was preparing to make its descent.

Algerian television broadcast images of the crash scene showing the broken carcass of the aircraft lying in a mountainous snowy landscape, at an altitude of 1,500 metres (5,000 feet).

"School notebooks and military duffle bags were also visible at the site of the crash," a source at the scene of the crash told AFP.

- Hercules 'normally extremely reliable' -

"Very bad weather conditions, involving a storm and heavy snowfall, were behind the crash," the defence ministry had said on Tuesday.

"A commission of inquiry has been created and sent to the scene to determine the causes and exact circumstances of this tragic accident," it added.

Flight specialist Kaddouche Maamar, quoted by Algerian daily El Watan, said the airport in Constantine is particularly difficult because of the high surrounding terrain.

He said that Hercules aircraft were normally extremely reliable, adding: "We can never eliminate all the risks linked to a crash."

Another Algerian newspaper, El Khabar, quoted a security source as saying the pilot had contacted an air base in Oum El Bouaghi several minutes before the crash, requesting clearance for an emergency landing.

President Abdelaziz Bouteflika announced three days of national mourning beginning on Wednesday, praising the soldiers who perished in the crash as "martyrs".

"It is a painful test for the Algerian people, who have just lost some of their brave and loyal children" as they were returning home, Bouteflika said in a letter of condolence to the families of the dead.

Tamanrasset, where the flight originated, lies in Algeria's far south near the border with Mali, and is the main base for the country's southern military operations.

It is 1,500 kilometres (950 miles) from Constantine, and was the site of Algeria's worst air disaster in March 2003, when an Air Algerie passenger plane crashed on takeoff after an engine caught fire, killing all but one of the 103 people on board.

The same year, another C-130 crashed in a residential Algiers neighbourhood, killing 20 people -- four crew members, eight passengers and eight people on the ground.