Police are questioning one person after a man was found unconscious in downtown Calgary early Monday morning.

Investigators say they were called at about 2:25 a.m. after a man in his 30s was found suffering from a head wound.

When officers arrived at the scene at 11 Avenue and 1 Street S.E., they found the victim, who was unconscious.

Paramedics took him to Foothills Hospital, where he is listed in critical condition.

Police have one man in custody for questioning, but no charges have been laid so far.

Investigators say he is not considered a suspect at this time, but may have information about what took place.

The investigation is ongoing and southbound Macleod Trail between 10 and 11 Avenues has been shut down for the incident.