A suspect in the unprovoked shooting of a St Louis, Missouri police sergeant was shot and killed in a gun battle with other officers early Monday.

The heavily-armed shooter, aged about 19, fired directly from his car into a police cruiser that was alongside him in traffic at about 7:30 p.m. local time (8:30 p.m. ET) Sunday, the city’s police chief Sam Dotson told reporters.

Police chief Sam Dotson briefed reporters. St Louis Police Department

A 46-year-old officer with two decades’ service was hit and was later described as being in a critical but stable condition.

Later, the suspect fired at officers who were following him. He ran but was pursued and fatally shot, Dotson said.

“We were tracking him, we came to this neighborhood, we found him, he shot at police officers again,” the chief said.

The suspect, described by Dotson as an African-American man born in 1997, had been involved in a number of violent crimes over the weekend and was carrying several rounds of ammunition.

Shot officer is in critical but stable condition, and is expected to survive. Very encouraged that I was able to speak with the sgt. #fgs — MayorSlay.com (@MayorSlay) November 21, 2016

“We believe the suspect shot the officer earlier in the evening in fear of being recognized.”

St Louis mayor Francis Slay posted on Twitter that he went to the hospital to visit the wounded officer, who was in a "critical but stable condition and is expected to survive."

"Very encouraged that I was able to speak with the sergeant," Slay wrote.