Police say an armed suspect who shot at officers was critically wounded when officers returned fire.

The shooting happened in Ferguson amid a demonstration to mark one year since the death of unarmed black teen Michael Brown.

Fox News.com reported:

Chief Jon Belmar did not identify the suspect, whom he said was in "critical, unstable" condition at a local hospital. However, the St. Louis Post-Dispatch identified the man as 18-year-old Tyrone Harris Jr. Harris' father, also named Tyrone, told the paper that his son had just come out of surgery early Monday, and noted that his son and Brown "were real close."

In a statement released Monday morning, St. Louis County police said the suspect was one of at least two people who exchanged gunfire at around 11:15 p.m. local time along West Florissant Avenue. Belmar said that between 40 and 50 shots were fired in an exchange that lasted approximately 45 seconds, an amount he described as "remarkable."

Belmar said that officers had been tracking the suspect, whom they believed to be armed, during the protest. As the gunfire began, the unmarked van the officers were driving in turned on its emergency lights and began moving toward the suspect. Authorities said the man opened fire, striking the van multiple times.

The officers returned fire from inside the vehicle before pursuing the man on foot. Belmar said the man then shot again at the officers, all four of whom returned fire.

Four officers have been placed on administrative leave.