The car crashed into this roundabout in Swansea

South Wales Police confirmed that her life-support machine was switched off on Sunday evening.

Sharlene's mother, Christine, appealed for anyone with information about the incident - in which her daughter and another girl were left for dead by three youths who ran away from the crash - to come forward.

Sharlene, from the Morriston area of Swansea, had been travelling in the car with Amy Williams, 13, from the Loughor area, who remains in a critical condition.

One man has been questioned by police and released on bail, but police said they were still hopeful of making more arrests.

If anyone has got any information about the accident would they please come forward

Sharlene Banfield's mother Christine

Detective Inspector Julian Williams - who is heading the investigation - said the girls were left unconscious after the red Ford Orion car they were in hit a mini- roundabout in the early hours of Friday.

South Wales Police are still hunting three youths who were in the car but ran off, abandoning the girls after the accident.

Officers had spotted the red car on CCTV, driving erratically between Penllergaer and Gorseinon, but it crashed minutes later.

The two girls were thrown through the back windscreen of the car with the force of the crash.

'Needless accident'

In the hours following, Detective Inspector Williams said: "Because the girls are so critically injured, it's likely the youths also have injuries."

The incident happened at around 0247 GMT on Gorseinon Road.

The car involved had been reported stolen from the Loughor area of Swansea in the early hours.

Anyone with information is asked to contact South Wales Police is 01792 456999.