A protestor shot off a firework toward Boston police at the intersection of Tremont and Stuart streets following a mass demonstration against police violence on May 31, 2020. Photo by Chris Van Buskirk | State House News Service

Boston Mayor Marty Walsh denounced an outbreak of violence and vandalism following largely peaceful protests against police brutality that filled downtown streets Sunday night.

Dozens of storefronts in Downtown Crossing and Back Bay were smashed and looters made off with merchandise, as rioting continued past midnight. The initial protests attracted an estimated 20,000 people.

“The vast majority of people who came out were passionate and they were peaceful,” Walsh said at a Monday afternoon press conference. “What happened after the protests ended was an attack on our values, and an attack on our city and our people.”

Nine police officers and 18 civilians were taken to local hospitals, 21 vehicles were damaged, and 53 people were arrested as a day of protests originating in Nubian Square and Government Center concluded with rioting near Boston Common.

Rioters smashed windows of stores on Newbury and Boylston streets, some carting away merchandise, and spray-painting slogans on buildings.

Walsh denounced the “untold economic damage” to businesses and vandalism to public spaces and civic monuments.

“Some of those stores have been hurt badly by the pandemic and are just on the verge of coming back,” Walsh said. “They’re fighting to survive. Their workers are fighting to support their families.”

Police Commissioner William Gross said 26 of the 53 arrestees live outside Boston and sought to escalate the protest.

“Unfortunately others came hell-bent on destroying our city, our great city, our destination city, and we along with others, there were people from the community as well, were like, `No, you cannot destroy our city,’” Gross said.

Walsh said the MBTA made the decision to close subway stations, including Downtown Crossing, after the protests turned violent, although the agency came in for criticism from other city leaders like City Councilor Julia Mejia who said she personally had to rescue two young protesters trying to leave the area but who were stranded by a lack of public transit access.

“They made a decision because there were so many people in town to shut down the downtown stations,” he said.