A Sydney teenage girl has been stripped and beaten in a shocking incident, allegedly committed by three 13-year-old girls, who police say recorded the assault.

The 14-year-old girl was approached by three teen girls at a bus stop in Claymore, near Campbelltown, at 7pm yesterday.

Police allege the 14-year-old was forced to the edge of Longstaff Way while being held at knifepoint by the teens.

They then allegedly started to punch and kick her.

The teens then allegedly forced her to take off her clothes, whipping her with a phone cord while recording her.

The trip then fled, taking the girl’s top, pants, shoes and phone with them. 

Police say the girls were known to her.

PolAir was used to search for the girls allegedly involved, with three 13-year-olds arrested in Claymore.

Their phones were seized and the trio were taken to Campbelltown Police Station where they have been charged.

One 13-year-old was charged with aggravated robbery with an offensive weapon, an offence related to forcing a child to make child abuse material and possessing child abuse material.

The two others were charged with two offences, aggravated robbery with an offensive weapon, and aggravated causing a child 14 years or over to make child abuse material.

All three have been refused bail and will appear in childres court today.