Thousands of people are to rally outside a German hospital to pay tribute to a young woman, who was beaten into an irreversible coma, after she stood up for two underage girls during a fight at a McDonald's restaurant.

The 23-year-old student Tugce A. has been on life support at hospital in Offenbach, near Frankfurt, ever since she was viciously attacked outside the fast-food restaurant two weeks ago.

Her parents have reportedly decided to pull the plug to the machines that keep her breathing today - her birthday - after doctors said she is brain dead and has no chance of recovery.

However, the procedure has yet to take place.

More than 6,000 well-wishers moved by her situation are expected to gather in front of the hospital on Friday evening to pay tribute to her, according to a Facebook page named in her honour "Tugce showed courage, we show her our respect".

The page itself has drawn almost 90,000 likes, while an online petition for her to receive the Bundesverdienstkreuz (Federal Cross of Merit) has been signed by more than 49,000 people in a few hours.

The woman of Turkish origins was dining at a McDonald's 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.

They are also accused of demanding payment from Tugce's friends when they rushed to get some water for the student who was lying bleeding outside.

McDonald's has denied the accusations, saying that all staff behaved adequately.

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