At least four people have been shot dead at Cascade Mall, around 100km north of Seattle, Washington State Patrol reports.
The suspect, who the police say is still at large, has been described as a skinny Hispanic male who has black hair and was wearing a black shirt. He is believed to be aged between 20 and 25.
According to local media, citing state patrol officers, a number of people have also been injured in the incident.
Police officers have confirmed on social media that the shooter has fled the scene.
Skagit County Department of Emergency Management has urged people to avoid the area.
Reports suggest police and other emergency service personnel were called to the shopping centre in Burlington, Washington state, at around 7.30pm local time (4am CET). Shoppers described being put on lockdown shortly afterwards.
Emergency service workers are said to have entered the mall at approximately 8.15pm (5.15am CET) to begin treating the victims.
A potential motive for the shooting is as yet unclear.
It comes less than a week after a man was shot dead after stabbing nine people at a mall in central Minnesota. The FBI is investigating the knife attack as a potential act of terrorism.