Police and medics rushed to the scene, the Citrus Restaurant and Lounge at 1001 Fairview Ave North, at about 1:30 a.m. Saturday.
They found a chaotic scene, with a hostile crowd that was interfering with officers as they tried to attend to the three shooting victims.
All three victims were rushed to Harborview Medical Center with very serious injuries, said Seattle Fire Department spokesman Kyle Moore. None of the victims would tell officers what happened.
Witnesses told police the drama began with a brawl inside the lounge that quickly escalated, with patrons throwing glasses and bar stools at one another.
Bouncers threw several people out of the establishment, and the fight moved across the street to a parking lot. Gunfire broke out, leaving the three men with life-threatening injuries, said Seattle police spokesman Neil Lowe.
The first victim, a man of unknown age, suffered gunshot wounds to both arms and the left leg.
The second victim, a 30-year-old man, suffered multiple gunshot wounds. Medics were administering CPR as he was rushed to the hospital.
The third victim, a 24-year-old man, suffered multiple gunshot wounds to the stomach.
Relatives of one of the victims told KOMO News that he is expected to survive - but he may lose his leg.
Police said about 30 shots were fired altogether. Two cars had several rounds through their windshields, and a few rounds also struck the front of the club.
An investigation found gun shells at the scene, and one handgun was located away from the scene.
Police originally said some suspects were taken into custody, but they later said one or more shooters are still being sought. It is unknown whether the suspect or suspects fled in a vehicle or on foot, police said.
Neighbors in the area say they believe late-night drinkers are responsible for recent vandalism and car break-ins in the area - but they never expected an eruption of violence like they witnessed early Saturday.
"I'm frightened and appalled," says Margery Pentland, who lives with her husband on a boat at the marina right next to the Citrus Restaurant.
"Lots of crowds on occasion, lots of revelry, lots of stuff going on in the parking lot," says Margery Pentland. "But this is beyond anything that's ever happened before. This is way over the top."
Another neighbor who lives on a boat tells KOMO News that Citrus draws a rowdy crowd - and that an officer once told her he wouldn't be surprised if somebody got shot there.