Terrorism unlikely as French crash cause

France's interior minister has apparently ruled out a terrorist attack as the cause of the Germanwings air crash in the French Alps.

"The debris from the plane is spread over one and a half hectares, which is a significant area because the shock was significant," Bernard Cazeneuve told French radio station RTL the morning after the disaster, on Wednesday.

"But it shows that the plane did not appear to have exploded."

The theory of a terrorist attack is "not the theory we're focusing on", Cazeneuve said.

Nevertheless, the minister added cautiously that "all theories must be carefully examined until we have the results of the enquiry".

He said the black box that had been recovered from the crash site, which records the sounds and conversations in the cockpit, had been damaged and would need to be repaired "in the coming hours".

"The enquiry must begin today," stressed Cazeneuve.

Early on Wednesday, investigators began the grim task of sifting through the pulverised remnants of the Airbus A320, which smashed into the French Alps, killing all 150 people on board.

Their efforts are being hampered by the inaccessibility of the crash site, with helicopters finding it near impossible to land in the rocky and perilously steep mountain terrain.