A British father, mother and grandmother were shot dead and a seven-year-old violently beaten as her four-year-old sister hid under her family's dead bodies in the car during a camping holiday in the French Alps.
The man killed in the shooting spree, which is so far unexplained, has been named as Baghdad-born Saad El Hilli, 50, by AFP. The family are believed to live in Claygate, Surrey.
A four-year-old girl was found alive inside the car containing the bodies of those believed to be her father, mother and grandmother. A seven-year-old, believed to be her sister, lay badly beaten in the road.
Officers said the two girls were now under "extremely high protection".
A gendarme stands by the caravan where the slain British family were holidaying in a camp site of Saint Jorioz, near Annecy
The Telegraph reported that Mr Al Hilli is understood to have been the secretary of a Wiltshire-based aerial photography company, AMS 1087, since 2007 and the family had been in the UK for at least a decade.
Investigators discovered the unharmed girl among the dead bodies after being called to the massacre in the Haute-Savoie region.
It was not until police linked the car to the campsite that officers discovered there were two children in the group. Witnesses told police that they had seen the family with two children, not one.
This information was relayed to police at the scene who spotted movement in the vehicle at around midnight.
The elder girl, seven, was discovered lying on the road in a critical condition near the BMW people carrier while a male cyclist, named locally as Sylvain Mollier, suffered gunshot wounds and was found dead close by.
Benoit Vinnemann, who is leading the investigation, told the BBC: "The three bodies found in the car appear to be the father, mother and grandmother.
Annecy prosecutor Eric Maillaud added: "At the beginning of the investigation when the investigators got into the car they discovered a little girl, who was frozen still and uninjured."
"She could not tell the difference between the good guys and bad guys. She spontaneously began to smile and speak in English when the policeman took her in his arms and pulled her out of the car."
He added: "She had heard the noises, the cries but she couldn't say more, she is only four years old."
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."
Mr Maillaud said the critically injured seven-year-old was taken to the nearby Grenoble University Hospital where her condition had been stabilised following emergency surgery on her fractured skull.
Doctors have now said she is now out of danger, he added.
"We don't know when we will be able to question her and I would imagine she is in a state of shock," Mr Maillaud said.
French gendarmes stand guard near vehicles where a British family stayed prior to being found shot dead
Investigators have begun inspecting a caravan used by the family at the campsite Le Solitaire du Lac, at Saint-Jorioz.
One woman at the campsite said: "I saw the two women yesterday with the two little girls collecting apples. Everything seemed normal, but I didn't know them.
"It was the first year that they had been seen here. It is terrible. The atmosphere is heavy, nobody is speaking."
The Foreign Office said it was in close contact with the French authorities and seeking further information. The British deputy ambassador to France is on the scene.
A FCO spokesman said: "We are aware of the reports of the shooting and we are looking into these urgently."
Maillaud said 15 cartridges were found around the car and that a "very large number" of shots had been fired.
The firearm used in the spree is thought to be an automatic pistol, he added.