The parents of a German student have decided to take her off life support on her birthday, after doctors said she was left brain dead by a brutal beating at a McDonald's restaurant, local media have reported.

Known only as Tugce A, the victim, of Turkish origins, will turn 23 and die tomorrow after almost two weeks in a coma.

The circumstances that led to her demise have shocked Germany.

The student was dining at a McDonald's in Offenbach, near Frankfurt on a Saturday night, when a violent quarrel, involving three young boys and two girls reportedly aged between 13 and 16, broke out in the restaurant's toilet area.

Friends said Tugce left her table and stepped into the argument to quell it upon hearing the girls screaming for help.

The boys subsequently left the premises, but when Tugce also came out about an hour later, they were waiting for her in a parking lot.

An 18-year-old identified only as Sanel M, according to German privacy laws, reportedly punched her on the side of the head. The student fell, hitting her head on the floor, and entered into a coma.

Eyewitnesses have accused McDonald's staff of aloofness after they allegedly failed to intervene or call police as the fight broke out, also demanding payment from Tugce's friends when they rushed to get some water for the student who was lying bleeding outside.

"I don't understand why a girl has to come to the rescue of two young women that are in the toilet screaming because no one acts," a cousin of Tugce said, Die Welt newspaper reported.

McDonald's has denied the accusations, saying that all staff behaved adequately. The company said it provided water to the girl's friends within seconds and a member of staff also went outside to help, according the newspaper.

Tugce's parents have now decided to let her die, after doctors said there was no chance of recovery, DPA news agency reported.

Sanel M has been arrested by police and remains in custody.