Spokesperson Renee Witt said the 15-year-old boy and two other teens were confronted by three men between the ages of 19 and 20 when they walked out the mall.
An argument ensued and one of the men fired seven or eight round in the southeast parking lot of the shopping complex.
Seattle Fire spokesperson Helen Fitzpatrick said the boy was shot twice, once in the leg and once in the groin area.
The other two teens were not hurt.
The shooting victim was taken to Harborview Medical Center where he is listed in critical condition. His name has not been released.
Police said they have surveillance videos showing the three suspects and believe it is only a matter of time before they are identified.
Lt. Ron Wilson said the argument between the two groups had started inside the mall. Security guards eventually broke up the fight and escorted one group out of the mall through the south doors and the other through the east doors.
But the two groups met up again in the parking lot where their resumed argument escalated into a shooting.
One of the bullets hit the building.
"There's a mark above the doorway to Lenscrafters where the bullet actually hit the glass," said Nathan Munson, a witness. "We're lucky no one else was hit."
The shooting did not appear to affect the volume of shoppers at Northgate Mall today.
"When I come here shopping, they usually address the security concerns pretty well so I'm sure they're taking care of all the necessary precautions as far as the public safety," said Hank Chen, who was shopping at the mall Saturday.
But some other shoppers were a little more leery.
Said Emma Bogus: "It frightened me to come over here after what happened. ... This is broad daylight, it can happen to anybody."