Eight teenage girls have been charged with murder in the stabbing death of an elderly man in Toronto, Canadian officials said Tuesday.

Police Detective Sergeant Terry Browne told a news conference the girls -- who range in age from 13 to 16 years -- assaulted the 59-year-old man in downtown Toronto just after midnight Sunday.

He described it as "a swarming."

Little was known about the girls, except that they had connected through social media. "We don't know how or why they met on that evening in downtown Toronto," said Browne.

The girls were arrested in the vicinity shortly after the attack and several weapons were seized. Browne added that police believe they had been involved in another violent altercation prior to the murder.

The victim was treated by paramedics but died in hospital a short time later.

He'd been living at a Toronto shelter for the homeless after some recent "hard luck," but continued to be supported by family, said Browne.

Girls generally account for a minority of crimes in Canada, with boys twice as likely to engage in violent behavior, according to government statistics.