The sister of a 14-year-old girl allegedly gang-raped in Doonside has desperately called for calm as racial tensions escalate in Sydney's western suburbs.

Six men attacked the girl as she walked through Bill Colbourne Reserve on Saturday night, pinning her to a footpath and sexually assaulting her one by one for 30 minutes, police said.

The park where a 14-year-old girl was allegedly raped by a group of men on Saturday.

Police described the men as aged in their teens to early 20s and of "African" appearance, sparking fears of reprisal attacks between the local African community and the islander community to which the alleged victim belongs.

The girl's older sister said friends of her brother were encouraging him "to go out there and fight". She took to Facebook to beg friends and family to stay calm, saying "what we need is peace especially my parents and ... my baby sister".