Police were forced to disperse revellers at an out-of-control 15th birthday party last night.
About 70 people were told to move on by police after they arrived at a Briggs Court home in Beaconsfield shortly before 9pm.
The birthday party is understood to have been advertised through social media.
Officers detained six juveniles after deeming them at risk and moved them under Section 41 of the Children and Community Services Act.
One youth had to be taken to Fremantle Hospital for observation while the other five were taken to Fremantle Police Station before being collected by a responsible adult.
The force's new party bus was not used by responding officers.
A police vehicle sustained minor damage after it was damaged by a bottle thrown by an unidentified youth.