Authorities believe only one person fired the shots Friday night at Cascade Mall in Burlington, about an hour north of Seattle.
A search is underway for an armed man who headed toward Interstate 5 after the attack, said Sgt. Mark Francis, a spokesman for the Washington State Patrol.
Francis released a blurry surveillance photo of a man described as the suspect. His motive or relationship to the victims, if any, are unclear, he said.
The names of the victims were not immediately released.
Moviegoers asked to leave
Witnesses described chaotic scenes and confusion when the shooting started about 7 p.m. local time
Brandi Montreuil told CNN she was watching a movie at the mall when attendants suddenly told them to leave.
"I didn't know anything," she said. "The theater attendant came in and apologized for stopping the movie and said they were asked to have everyone leave immediately."
At first, she thought it was a drill.
"But you immediately think about what happened in Aurora, Colorado, so you start moving faster," she said, referring to the 2012 shooting at a movie theater
that left 12 dead.
When they got outside, they saw police vehicles but no officers in sight, Montreuil said.
"We didn't know if it was a fire so we were looking for smoke of some kind. Then a few officers started canvassing through the crowds, asking if anybody saw anything."
An officer "with a large gun started yelling for people to leave and fast," she said.
Armando Patino said he was working at a T-Mobile store near Macy's when he heard the commotion.
"Out of nowhere I just hear somebody yell and then after that, I turn around and just look at the Macy's and I just hear shots," Patino told CNN affiliate KOMO-TV
"I hear one shot and then stand kinda still and like two three other people start running out saying, 'gun.' "
Some people dashed out of Macy's, unsure of where to go.
"I just moved them into the (T-Mobile) store," Patino said.
"We went in the back where we have a door ... and we just stayed there until they told us to evacuate."
Mall searched throughout night
A bus transported survivors to a nearby church as authorities warned people to stay indoors and avoid the mall area.
Dozens of cars were left behind in the parking lot, according to Francis of the State Patrol. He said it's unclear if one of them belongs to the gunman.
Those who left their cars at the mall were told to check back the next day.
"Cascade Mall still an active scene," the Skagit County emergency office tweeted. "Stay alert. Call 911 if you see anything."
Officers using K-9 units searched the 434,000-square feet mall throughout the night, including in secure rooms, authorities said.
FBI assisting with intelligence review
Authorities released a photo of a man they said was the shooter, saying he prowled the mall armed with a rifle.
"Here is the shooter. We believe just one shooter. ... Armed with rifle," Francis tweeted. A manhunt is underway as police work on a few leads.
Washington State Trooper Rick Johnson told CNN they got reports that the suspect was behind some buildings headed to the freeway.
"They're canvassing the area right now, and ... (he) has not been located at this time," Johnson said early Saturday.
The FBI office in Seattle is helping with a review of intelligence. There's no information to suggest additional attacks were planned in the state, it tweeted.
'Stay close to friends and loved ones'
Washington Gov. Jay Inslee said law enforcement officers were working to locate the shooter, and urged residents to follow instructions.
"Follow detour warnings, stay close to friends and loved ones as we await more information and, hopefully, news of the suspect's capture," he tweeted.
Inslee sent his condolences to the families of the victims and prayers to those injured.