A military aircraft has crashed into a mountain in Algeria, killing 77 people and leaving just one survivor.

The Hercules C-130 was carrying military personnel and their families when it crashed in the Oum El Bouaghi region, about 400 kilometres from the capital Algiers.

Officials say the plane crashed into a mountain and exploded amid bad weather and strong winds.

"Several bodies were burnt to ashes and could not be identified," one official told Reuters by telephone from the area.

Initial reports suggested the death toll had climbed above 100, but the Defence Ministry now says 77 people died.

A map of Algeria locating the Oum El Bouaghi province, where the military transport plane crashed. ( Reuters )

The ministry gave no immediate explanation for the discrepancy.

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.

President Abdelaziz Bouteflika has 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, and lost contact with the control tower just as it was beginning its descent.

Tamanrasset, in the far south of Algeria, near the border with Mali, 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 crash is the worst in Algeria since 2003 when an Air Algerie jet crashed shortly after takeoff from Tamanrasset, killing 102 people.

The Defence Ministry has set up a commission to investigate the crash.

ABC/wires