Ottawa police are warning Bluesfest concert-goers to be mindful of their personal security aboard OC Transpo buses, after an alleged swarming on Saturday night involving at least five victims and more than 10 suspects.

The incident happened sometime around 11:30 p.m. aboard an OC Transpo bus at the Slater Street stop between Bronson Avenue and Bay Street, shortly after the Shawn Mendes concert at LeBreton Flats.

Ottawa police say several festival-goers got on the bus and were immediately held against their will, while a large group of suspects rifled through their personal belongings.

A 21-year-old woman was among those targeted by the suspects. CBC has agreed to withhold her name because she fears for her safety.

"They got really violent, tried to threaten us, tried to say they were going to fight us, beat us up, kept reaching into their pockets," she said.

The woman and her friends had just boarded the bus heading downtown — hoping to continue their night — when one of them was mugged.

"Our friend was targeted by a group of people and surrounded by them. His pockets were then completely emptied of his wallet and his phone and everything else," she said.

"He looked vulnerable and we were all having a good time and enjoying ourselves and he looked like an easy target."

No suspects in custody

Police said they received multiple calls from people aboard the bus, prompting six police cars to respond to the incident, along with just as many OC Transpo special constables.

A few men fled from the bus and were involved in a foot pursuit with the special constables, said Ottawa police Staff Sgt. Scott Pettis.

Police interviewed more than 10 suspects and some five victims, he said, noting that additional victims left the scene after telling police that they had had some of their possessions stolen as well.

Pettis said the bus was very crowded, with many concert-goers intoxicated after attending the festival.

"It was tough for witnesses who were deemed credible — meaning they were sober — to identify exactly who was involved," Pettis said.

Police have no suspects in custody, but robbery detectives will continue to investigate at a later date, he said.

OC Transpo special constables arrested several men who violated transit rules, according to Pettis.

Officers are hoping to receive additional video surveillance footage and to speak with other witnesses who might come forward.

Pettis also urged festival-goers to be mindful when taking public transit to and from Bluesfest.

"It's our belief that this was a calculated, organized event by these suspects," he said.

"People should be careful about where they store their personal belongings and whatnot and just be aware of their surroundings and their personal security."