Much of the city of Seattle was in mourning on Monday as residents paid tribute to the three lives that were lost during a deadly street gunfight the day before.

The city's mayor was among dozens who gathered at a local fountain for a candlelight vigil, while online fundraisers for two of the victims received tens-of-thousands of dollars in donations.

Those who died on Sunday at the annual Bite of Seattle food festival were Junior Cee Niko Semo, 19, Carlos Israel Sanchez Villalba, 44, and Ashley Whitehead, 56. At least four others were injured.

A GoFundMe for Villalba described him as "a devoted husband, loving father of three, and a loyal friend who would do anything for anyone".

"His kindness and generosity touched countless lives, and everyone who knew him remembers his gentle spirit and willingness to help others," the write-up said.

"His sudden passing has left his family heartbroken and facing an uncertain future."

The family has said the funds will go towards funeral expenses and help fill the void in his absence. He leaves behind a wife and three children.

Sunday was the final day of the annual three-day free food festival, which draws some 350,000 people each year.

Family members of Ashley Whitehead said she was standing in line with her daughter, waiting for cotton candy, as gunshots rang out and ended her life.

She died in hospital during surgery, after exchanging "heartfelt 'I love you's with her eldest daughter", her family said in the GoFundMe page launched after her death.

Whitehead was described as "a lover of life, art and family".

"Family was everything to Ashley - she had recently moved to the west coast from Alabama to be closer to Zoie," the writeup said, referring to her eldest daughter.

At the vigil on Monday evening, people laid flowers and lit candles as they gathered in grief. There was a call for a moment of a silence.

"This is not acceptable," Seattle Mayor Katie Wilson said, condemning gun violence in the community. "No father, no parent should have to bury their child."

Washington state Governor Bob Ferguson said in a social media post that the community was shocked and "struggling to make sense of how an iconic community celebration could end in gunfire".

Police suspect the third deceased victim, Junior Cee Niko Semo, was involved in the gunfight. Neither of the other two victims are suspected of any crimes.

The authorities believe at least two other suspects were involved, including a 15-year-old, who is in custody, and a third unidentified person.

Police said at a news conference on Tuesday that the attack was a "targeted" act of gang violence. They are still investigating what groups may have been involved.

Three guns have been recovered from the scene of the shooting, including an unregistered "ghost gun" that has an extended 33-bullet magazine, and a pistol with a fully automatic switch.

Seattle Police Chief Shon Barnes said they want to speak to one person who went to hospital with a gunshot wound but left before speaking to police. They have been unable to obtain this person's ID, he added.