Images began circulating on social media over the weekend of a little girl who was coughing and crying while bystanders poured a milk-like substance into her eyes to flush out the chemicals.
The footage also shows protesters confronting the officers allegedly involved in spraying the girl and asked for their badge numbers. One officer allegedly refused to give the protesters his badge number.
Buzzfeed News spoke with Evan Hreha, who filmed the scene. Mr Hreha said the protest was peaceful prior to the macing incident. He recalls a priest leading a prayer session before police rushed the crowd and began spraying people.
"The next thing you know, the little girl and others were running out screaming. They had been maced and that's when I started filming," Mr Hreha said. "Everybody on the left side of the street we all saying that is was officer Campbell [who used the mace]."
Mr Hreha said he walked over to the police officers and asked for "Campbell." An officer with the last name Campbell was present, and footage from the protests shows he was carrying mace, but the officer did not respond to Mr Hreha's questioning.
In the video, other officers questioned by protesters give their badge numbers when asked.
The protesters who witnessed the scene and posted the video are calling on people to file complaints with the Seattle Police Department's Office of Police Accountability.
Seattle police said they'd received many complaints about the encounter and confirmed they will investigate the incident.
"As the mayor made clear during today's press conference, all uses of force by SPD officers will be investigated accordingly, and officers will be held accountable for inappropriate uses of force. Retaining and building community trust that SPD and partners have worked tirelessly to improve is absolutely paramount," a police spokesperson said.
Seattle's city council members spoke out Monday against the use of mace and excessive force by the city's police.
"I personally witnessed the unacceptable escalation of violence by the Seattle Police Department," Councilwoman Kshama Sawant said during the city council's Monday briefing. "We have had hundreds, if not thousands of accounts from ordinary people of unacceptable conduct from the SPD. Seattle police officers indiscriminately used tear gas, mace, flash bang grenades and other types of excessive use of force on the peaceful protesters."