Police arrested one suspect and are searching for another over a shooting near Seattle's Space Needle that killed at least three people and wounded four others, including a toddler Sunday.

Assistant Police Chief Tyrone Davis said shots were heard around 6 p.m. (1 a.m. GMT) and "there were two people who we believe were shooting at each other." Two weapons were recovered.

There is "no outstanding threat to the community," he said.

Seattle Police said two people died at the scene at the Seattle Center and a third died in hospital.

Washington Gov. Bob Ferguson said State Patrol SWAT officers had been deployed to assist local police.

"My prayers are with the families of the victims, and the responders as they work to keep people safe," he said on X.

Mayor Katie Wilson said the shooting was "an act of horrific violence."

"Our attention belongs to the people whose lives were taken, those fighting to recover, and the families beside them," she said in a statement.

Wilson also expressed her thanks to "the Seattle police officers who responded to the scene and took a suspect into custody."

Four patients were being treated at the trauma center facility at Harborview Medical Center, according to spokesperson Susan Gregg: a child, a woman of unknown age who was in surgery, a 23-year-old man and a 39-year-old woman.

One of them did not survive their injuries, Davis said, without identifying the victim.

Another victim arrived later at the University of Washington Medical Center with a gunshot wound, according to Davis.

Those that remained in hospital, including the toddler, were in a "stable condition," he said.

Several witnesses told Seattle television station KIRO they heard multiple shots before running away.

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

"We started running. I didn't know. I didn't look where the person was going. I just heard everything," a witness said.

The shooting took place during the "Bite of Seattle" summer festival celebrating local businesses and food vendors.