Bristol Street – one of the main routes into the city centre – has been cordoned off by police.
It is closed southbound from the Pagoda Island to Bromsgrove Street and is expected to remain closed for some time.
Acting Ch Insp Michael Clarke appealed for anyone with information about the shooting to contact West Midlands Police.
“This happened in a busy nightclub, on one of the main roads out of Birmingham, so it’s vital that we hear from anybody who saw what happened or who may have captured it on dashcam as they went past,” he said.
“If you were in the club at the time and saw what happened, or recorded any footage from inside the venue, we need to hear from you urgently.”