An 18-year-old man has died after a stabbing in Calgary's Beltline neighbourhood Saturday morning.

Police say they were called to an alley along 10 Avenue S.W. just before 3 a.m. MT. There was a large group of people gathered at the scene, but it's not clear at this point how many were actually involved in the attack.

"On arrival we determined a male patient ... had sustained multiple traumatic injuries as a result of some sort of assault and altercation," said Stuart Brideaux, spokesperson for Calgary EMS. 

The victim died around 10 a.m. And while details are limited, police believe he was involved in at least one altercation outside a downtown bar.

Detectives are working to determine who was involved in the assault and when the victim suffered the fatal injuries.

Police say a 20-year-old man is in custody and they are interviewing several witnesses.

No charges have been laid.