Police failed to spot the terrified youngster in the British-registered BMW car until midnight  - eight hours after the shooting took place.

A French source said she was found hiding underneath her mother's legs. The two other bodies are believed to be those of her father and grandmother.

It is not known whether she crawled under the bodies to hide or was left trapped when they fell on top of her.

The family were believed to have been staying at the Saint Jorioz camping site. A British family reported their disappearance to police on Wednesday night.

Besides the British family, the fourth victim of the deadly shooting was a cyclist, said to be a local man.

The little girl, who spoke English, was found hiding under her mother's legs said Eric Maillaud, a prosecutor in the Haute-Savoie area of eastern France.

Her eight-year-old sister was wounded in the attack and rushed by helicopter to hospital in critical condition, officials said. She was said to be in a more stable condition early Thursday but set to remain under treatment for several days.

Some 15 spent bullet casings from an automatic pistol were found at the crime scene.

The four-year-old girl was discovered by special investigators long after police had sealed off the area.

'She was hidden under the bodies for some eight hours and didn't move for the whole time,' and was not discovered until the investigators from the gendarmerie reached the scene, Maillaud said.

The body of the male cyclist was found a few yards from the car, which was in a remote woodland car park near the town of Chevaline, close to the mountain resort town of Albertville.

One theory was that the cyclist saw the shooting and was killed to silence him.

Dozens of bullet cartridges littered the scene.

The bloodbath was discovered by a second cyclist – thought to be British – who stumbled on the horror scene at 4pm (3pm UK time).

The area is close to the Swiss and Italian borders. Nestled in hills next to Lake Annecy, in France’s Haute-Savoie region, it is a magnet for British holidaymakers.

The girl was found a short distance from the car, bleeding from ‘at least three’ gunshot wounds, according to a source.

She was airlifted in an air ambulance to Grenoble’s CHU hospital where she underwent surgery. At one point, police incorrectly announced she had died.

Eric Maillaud, the investigating prosecutor from Annecy, said: ‘It is a dramatic crime scene like we see on the TV. We are employing all necessary means to investigate. Two men and two women are the victims. The car is a British-registered BMW estate.

‘One of the male victims was a cyclist. He was found near his bike in his cycling gear. The other man was in the driving seat of the car. The two women were in the back of the car. There is a large number of gun cartridges at the crime scene.’

Didier Berthollet, mayor of Chevaline, said that ‘the victims were not from the village’, adding that locals had told police they had seen a car speeding past between 3pm and 4pm. At least 60 policemen sealed off the area and a helicopter was circling overhead. There were no reports that anyone had been arrested.

The attack took place close to Doussard, which is hugely popular with British holidaymakers during the summer months. Police have not yet confirmed the nationalities of the deceased, but they are thought to be from the UK because of the BMW’s registration plates.