St. Louis police said a group of agitators disrupted several downtown St. Louis businesses Sunday evening after a peaceful protest had concluded earlier in the day.

Around 8:45 p.m., several reports of broken windows were reported by St. Louis Metropolitan police. Businesses were vandalized at the intersection of Olive and 10th Street and moved toward Washington Avenue. Police soon responded to help contain the crowd of an estimated 100 agitators, forming police lines in order to keep them contained.

Orders were given to the crowd to disperse near the intersection of Tucker Boulevard and Pine Street. Police said the protest was "no longer" peaceful and declared an unlawful assembly.

Around 11:30 p.m., boxed in in a group of demonstrators at the intersection of Tucker Boulevard and Pine Street. Several people were placed under arrest during the incident, although police have not yet given a number.

PHOTOS | Downtown St. Louis property damage

One bike officer was transported to an area hospital to be treated for a leg injury. The injury was not classified as life-threatening. Several St. Louis County officers were exposed to unknown chemicals and treated by the St. Louis Fire Department.

According to 5 On Your Side's Christina Coleman, patrons on Sushi Ai on the 900 block of Olive Street were disrupted by an object that shattered the front window of the restaurant. One witness said restaurant staff directed customers into the kitchen to protect them from the incident happening outside.

A separate, peaceful protest was held Sunday afternoon in front of the St. Louis Metropolitan Police Department on the 1900 block of Olive Street. Protest leaders disbanded the group around 7 p.m.

WATCH: Mayor Krewson, St. Louis police give an update on Sunday's protests

This is a developing story.