A military aircraft carrying 78 people crashed in Algeria's mountainous northeast with just one survivor on Tuesday, in one of the country's deadliest air disasters, the defence ministry said.

The C-130 Hercules aircraft, which came down in the Oum El Bouaghi region, was carrying 74 passengers -- soldiers and their families -- as well as four crew members, the ministry said.

The figure was far lower than the 103 people originally reported to be travelling on the C-130 Hercules transport aircraft by security sources and state media.

The ministry gave no immediate explanation for the discrepancy.

By early evening the emergency services had recovered 76 bodies from the crash site, including the remains of four women.

The sole survivor was taken to a military hospital in the flight's intended destination, the city of Constantine, east of the capital, suffering from head trauma, public radio reported.

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

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

The aircraft slammed into Mount Fertas in the Oum El Bouaghi region at around midday (1100 GMT), state media quoted army spokesman Colonel Bouguern as saying.

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

Nearly 250 emergency personnel were deployed to the crash site despite the difficulties caused by the mountainous terrain and wintry conditions, the ministry added.

The recovery teams located one of the aircraft's two black box flight recorders, Algerian newspaper El Watan reported on its website.

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

Extra troops and equipment have been stationed there in recent months as part of efforts to beef up surveillance of Algeria's frontiers with Mali and Libya, following a deadly hostage-taking by Islamist militants at a desert gas plant in January last year.

The city lies 1,500 kilometres (930 miles) from Constantine, and was the site of Algeria's worst ever air disaster in March 2003.

In that accident, all but one of 103 people on board were killed when an Air Algerie passenger plane crashed on takeoff after one of its engines caught fire.

The sole survivor, a young Algerian soldier, was left in a critical condition.

In December 2012, two military jets conducting routine training operations collided in mid air near Tlemcen, in the northwest, killing the pilots of both planes.

A month earlier, a twin-turboprop CASA C-295 military transport aircraft, which was carrying a cargo of paper for the printing of banknotes in Algeria, crashed in southern France.

The five soldiers and one central bank representative on board were all killed.