A girl was severely bashed in a brawl with other girls at a Sydney railway station yesterday but nearby CityRail security guards declined to intervene.

The alleged attack took place when a group of girls between 13 and 15 set upon another girl of about the same age at Cabramatta station, in Sydney's south-west, during afternoon peak hour.

Commuters were on their way home, and CityRail security guards were patrolling nearby.

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A witness, who did not want to be named, described the girls as "fighting like savages".