The 26-year-old lone suspect, who was not a student, entered an academic building of Seattle Pacific University in late afternoon and shot three people, police said. (Agencies)
He was disarmed as he paused to reload his gun and was pepper-sprayed by a student security guard. It was not clear how the fourth victim was injured.
"Other students jumped on top of them, and they were able to pin the shooter to the ground until police arrived" minutes later, police Captain Chris Fowler said on the scene.
The shooting comes amid a protracted debate in the US over the extent of gun control regulations after a series of shootings in public places such as schools and theaters.
On May 24, a 22-year-old gunman killed six people before taking his own life in a rampage across a California college town.
One eyewitness, Chris Howard, a 22-year-old junior at the university, said he was in a classroom when one of the male victims rushed in, bleeding from the neck and told students to lock the doors.
Stepping outside the classroom moments later, Howard recounted, he saw the gunman lying on the floor with the student security monitor on top of him, surrounded by bullet shells, and saw a second victim with a tourniquet tied around a bleeding arm, being assisted by another student.
He was armed with a gun and a knife and extra ammunition, police said.
The suspect, whose name was not released, was arrested and could face a murder charge, Fowler told an evening news conference.
A representative of Harborview Medical Center in Seattle said four patients from the shooting were brought to the hospital and that one, a man in his 20s, had died.
Two other men, aged 22 and 24, were listed in satisfactory condition, and a 20-year-old woman was listed as critical and undergoing surgery, the hospital official said.
Police later said there were no other victims.
Further details of the shooting in the upscale Seattle suburb of Queen Anne, a normally quiet residential neighborhood, were not immediately clear, and authorities did not offer an explanation for any motive behind the gun violence.
Another student, Blake Oliveira, 21, who was taking a physics course in Otto Miller Hall at the time, said he heard a gunshot outside the classroom, followed by the sound of running footsteps, which he presumed to be the gunman.
His professor instructed the students to stay put in the classroom, and the door was locked, Oliveira said.
The school said on its website that the campus was placed on a security lockdown as a result of the shooting. The lockdown was later lifted.
Seattle Pacific University is a Methodist liberal arts college about 4 miles (6.4 km) north of Seattle's downtown, with about 4,000 students enrolled.
The college website said students are subject to disciplinary action for such behavior as extramarital sex or homosexual activity and for the possession or use of alcohol.
Students could be seen embracing and otherwise consoling one another on campus, some crying as they recounted hearing a gunshot. An evening prayer service was being held at a campus church.
"We're a community that relies on Jesus Christ for strength and we'll need it at this time," said Seattle Pacific University President Daniel Martin.
The 26-year-old lone suspect, who was not a student, entered an academic building of Seattle Pacific University in late afternoon and shot three people, police said.