The 35-year-old victim was hit in the abdomen outside the Rainbow Warehouse club in Digbeth High Street in Birmingham at 11.47pm on Saturday. West Midlands Police said the man was taken to hospital where his condition is critical.
A force spokesman said: “His injuries are life-threatening and his family have been informed.”
Detective Inspector Justin Spanner, leading the investigation, said: “This is a very serious crime which must have been very frightening for clubbers to witness.
“Resources from a range of West Midlands Police departments responded to the initial call and we continue to make use of their expertise as the investigation moves forward.”
He added: “The motive for the attack remains unclear but initial enquiries indicate this was a targeted attack and that the gunman escaped on foot.
“We’ve been working hard to reduce gun crime across the region but crimes like this – no matter how rare they are – tarnish Birmingham’s reputation as a great place to enjoy a fantastic night out.
“If we are to understand why this shooting occurred and bring those responsible before the courts, I need anyone who was in the area at the time and has not yet spoken to police to get in touch.” Firearms officers were quickly on the scene, backed by a police helicopter and dog teams, after reports of the shooting came in.
The area outside the club and surrounding roads remained cordoned off as forensics teams continued the search for clues.