Officers were notified after gunshots were heard near Beethoven Street at around 7.44pm and duly arrested a man on suspicion of attempted murder.
The man who was shot was airlifted to hospital by the London Ambulance Service while paramedics also attended to a 19-year-old stab victim and a third man, 29, who was also injured.
Both were also taken to hospital but neither was thought to be in a serious condition.
Investigators subsequently cordoned off Beethoven and Bruckner Street while officers in protective clothing examined the area.
The Met also authorised a Section 60 Order empowering them to carry out stop and search activities across North Westminster from late last night to 8am on Monday morning.
Detectives from the Met’s Specialist Crime (Trident) unit are continuing their investigation and are asking anyone with any information on the violence to come forward by calling 101 or contacting them on Twitter @MetCC, quoting Cad 7211/13JUN.
In another incident on Sunday evening, a teenager was stabbed in Shadwell, East London, while Saturday night saw a 13-year-old boy in Putney stabbed, as well as the shooting of six people in Brixton.