The shooting occurred at a party inside a building in the city’s downtown area in the early hours of Sunday.
"It’s every parent’s worst nightmare tenfold," St. Louis Mayor Tishaura Jones said during a Sunday press conference as quoted by US media. "My heart goes out to all of the families in pain today."
A 17-year-old male was killed, and nine other people, identified as male and female teenagers between the ages of 15 and 19, were injured, St. Louis Police Chief Robert Tracy said as cited by US media on Sunday.
According to US outlets' reports, a juvenile suspect is in custody. The motive for the attack is under investigation.