Seattle police are still searching for a second suspect following a shooting at a food festival on Sunday that killed three people and left several others injured.

Police say two suspects were shooting at each other. One, who is 15 years old, is in custody, and officials believe there is no threat to public from the second, who has not been identified.

Shots rang out at around 18:00 local time (01:00 GMT) at the Space Needle – one of the city's most popular tourist spots – and as the annual Bite of Seattle food festival drew even more people to the area.

Two deaths were confirmed at the scene, and one person died later in hospital. A two-year old boy was among those injured.

The three people who died were a 19-year-old man, a 44-year-old man, and a 56-year-old woman, according to the authorities. Four of the injured were taken to hospital in a stable condition, while a fifth chose not to go.

Police chief Shon Barnes told a press conference on Monday it was possible that one of the individuals killed was the second shooter.

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

Videos shared online showed people crouched on the ground, taking cover behind pillars and shelves of merchandise in the Space Needle's lobby during the shooting.

Several witnesses told a local TV station affiliated to CBS News, the BBC's US partner, that they heard multiple shots before running away.

"At first, thought there were fireworks, and then everybody flooded and ran past us," Nick Bate told the TV station.

Leanne Coles another witness told the station she used the Space Needle to try to keep track of where she was.

"Everybody started running, and so we just ran too, and we ran through the garden and we ducked and we decided to keep running with the crowd," she said.

Faith Adia Hunter told Associated Press that one of the shooters was near her and her friends when they heard the shots, sending them fleeing for shelter in the Seattle Children's Museum.

"We were right next to him when it started so we took off running," she said. "So, we took off running too into the building with the crowd."

The Seattle Police Department said an investigation remains ongoing and urged the public to avoid the area.

Mayor Katie Wilson said in a statement that she wanted to "thank the Seattle police officers who responded to the scene and took a suspect into custody".

She had originally announced two suspects had been taken into custody before updating her statement later on Sunday evening.

Police are questioning the "young person" they took into custody, Assistant Seattle Police Chief Tyrone Davis said, noting that two guns were recovered at the scene.

Representatives for Seattle and Washington state have condemned the shooting as an act of "senseless violence".

"My prayers are with the families of the victims, and the responders as they work to keep people safe," Washington Governor Bob Ferguson said on social media.

Congresswoman Pramila Jayapal, who represents Seattle, added: "Our hearts go out to all those impacted by this senseless violence," she wrote on social media.

"We are in close touch with Seattle Mayor Katie Wilson and Governor Bob Ferguson, and co-ordinating across multiple levels of government to get updates on the situation."

Wilson also condemned the shooting as an "act of horrific violence".

"Impacted families are living through the worst moment of their lives, and an entire community is trying to understand how a gathering built around culture, connection, and joy ended in gunfire."

"Tonight, our attention belongs to the people whose lives were taken, those fighting to recover, and the families beside them," she added.

"Seattle grieves with you, and we will stand with you in the difficult days ahead."