Three teenage girls have been charged with assault after two separate violent attacks took place on Metro Vancouver's transit system.

Metro Vancouver Transit Police say the assaults happened on July 11, the first of which was on board a SkyTrain while it travelled from New Westminster to Surrey.

Police say a 16-year-old student was attacked by the three suspects after she tried to prevent one of them from prying open the doors while the train was moving.

The attackers are accused of punching and kicking the girl, then dragging her by her hair before other passengers and SkyTrain attendants in Surrey were able to help her.

Police say the second attack happened about three hours later, when the three boarded a bus and surrounded an 18-year-old woman following a verbal exchange. They punched and kicked the victim and pulled out clumps of her hair.

Officers who were called to the scene identified the suspects as a 13-year-old and a 17-year-old from Surrey, as well as a 15-year-old from Abbotsford. All three have been charged with assault causing bodily harm.

The suspects cannot be named under the Youth Criminal Justice Act.

Police say while they would never ask bystanders to put themselves in harm's way, the intervention by the other passengers to help the victims in the attacks should be acknowledged.