Toronto police have arrested one of two men accused in a violent sexual assault in a downtown condo building.

Investigators say the incident happened shortly after midnight on Wednesday when a 19-year-old woman was entering an elevator in the condo building.

They allege two men got into the elevator behind her and robbed her of her cellphone at gunpoint.

Police say the men then allegedly violently dragged the young woman out of the elevator and sexually assaulted her in a stairwell.

Police say a 24-year-old Toronto man is facing 11 charges, including two counts of sexual assault with a weapon and two of aggravated sexual assault.

Officers are still looking for a second 24-year-old man.