A four-year-old British girl was found alive underneath the bodies of her parents around eight hours after a brutal massacre in the Alps, French authorities have said.

And a seven-year-old girl, thought to be her sister, was found violently beaten and is fighting for her life. The four-year-old lay undiscovered as police waited for forensic experts to arrive at the scene from Paris.

A man and two women - believed to be the girls' mother, father and an older relative - were in the British-registered BMW, which was riddled with bullets. The man, in his fifties, had been behind the wheel at the time of the attack.

Public prosecutor Eric Maillaud said a British cyclist stumbled upon the shocking scene and spotted the seven-year-old lying in the road with horrific injuries. He said: "She appeared to have been violently beaten to the head and she had many brain injuries. The cyclist immediately placed her in the recovery position and called for help."

He reported four people dead - the three family members in the car and another cyclist who also suffered gunshot wounds and was found lying close to the vehicle. But the four-year-old remained undiscovered under her mother's body until midnight - some eight hours after Wednesday's shooting.

Mr Maillaud said she was "terrorised, motionless, in the midst of the bodies". He said: "As soon as the first forensics began, we were able to open the vehicle, and it was at that moment we discovered the little girl, around four years old, that nobody had seen, because she hadn't moved, completely in shock and completely frozen."

He said the girl was spotted late in the day because police immediately sealed off the area in the aftermath of the killings and, owing to the gravity of the operation, waited for back-up to come from Paris before they examined the scene.

The family had been holidaying in a caravan at the Le Solitaire du Lac campsite in nearby Saint-Jorioz, since the end of last month. Their BMW was discovered surrounded by spent bullet cartridges in a car park on the outskirts of a forest near Lake Annecy, a picturesque region popular with tourists.

It was not until police linked the car to the campsite that officers discovered there were two children in the group. This information was relayed to police at the scene who spotted movement in the vehicle at around midnight. Police are "almost certain" they know the identity of the vehicle's driver and believe he has lived in Britain for "at least a decade", Mr Maillaud added. The cyclist who reported the shooting is thought to be a retired man who was familiar with the area and was a regular visitor.

Foreign Secretary William Hague later tweeted: "Terrible, tragic shooting in France. British Embassy team on the scene. Our thoughts are with the young girls who survived and the family."