Two attackers were reportedly dressed in Santa costumes, witnesses told CNN Turk, when they opened fire in the Reina club in the Ortakoy area of the city. (Disputed reports are flying that it was only one Santa or there were no Santas. Stay tuned.)
One civilian and one police officer were killed and several wounded, NTV reported.
There were reportedly several hundred people in the club, which is among the city's glitziest nightspots.
Police cordoned off the area about 2 miles away from the nightclub as multiple ambulances rushed to the scene.