Police were first called to the downtown apartment building at 1263 Barclay Street near Bute Street around 6:45 p.m. PT.
When they arrived they found seven people suffering from stab wounds. Three men and three women were rushed to hospital with serious injuries. One person was treated at the scene.
Shortly afterwards a 33-year-old Vancouver man was arrested inside the building and taken into custody, said Sgt. Randy Fincham.
"It was a very vicious, scary, very serious attack." he said. "It is early in the investigation and the motive for this violent attack is unknown."
Fincham said it did not appear that the suspect lived in the building.
"This appears to be completely random at this point. This attack does not appear to be related to any activity within the building itself."
Fincham said the victims' ages range between 20 and more than 60, and they did not appear to know each other or their attacker.
Five of the victims are in serious but stable condition, but one woman in her sixties was in critical condition.
"Detectives from the Vancouver Police Major Crime Section and the Forensic Identification Unit have been called out and they will be at the scene throughout the night," said Fincham.