Nearly an hour after first reporting the incident, police said on their official Twitter feed that officers still have "no sightings of male with weapon."
Everett police spokesman Aaron Snell told KOMO-TV there are no reports of any shots fired or any injuries.
Snell says several people called police Thursday evening to report an armed man at the sprawling plant where Boeing builds wide-body jets ranging from the 747 to the 787. Numerous police units responded.
Boeing Co. spokesman Doug Alder says the company is "taking all precautions" until officials know what's going on. He declined to specify those precautions.