FERGUSON, Mo. » Police arrested more than a dozen people in Ferguson on Monday night after protesters blocked traffic during a fourth consecutive night of demonstrations marking the anniversary of the fatal shooting of 18-year-old Michael Brown.

The gathering came about 24 hours after a demonstration along West Florissant Avenue that was interrupted by gunfire and a police shooting that left an 18-year-old critically injured, setting the St. Louis suburb on edge.

St. Louis County Executive Steve Stenger declared a state of emergency, which authorized county Police Chief Jon Belmar to take control of police emergency management in and around Ferguson.

By early Monday evening, hundreds of people had gathered. They marched up and down West Florissant, the thoroughfare that was the site of massive protests and rioting after Brown was fatally shot last year in a confrontation with a Ferguson police officer.

The protesters chanted, beat drums and carried signs. When some in the group moved into a traffic lane, officers in riot gear forced people out of the street. Some demonstrators threw water bottles and other debris at officers.

Belmar told The Associated Press: "They’re not going to take the street tonight. That’s not going to happen."

More than a dozen people were arrested.

Ferguson resident Hershel Myers Jr., 46, criticized the police response as aggressive and unnecessary.

A military veteran, he added, "It’s wrong for me to have to go overseas and fight with Army across my chest, but we can’t fight on our own street where I live."

By 1 a.m., the crowd and police presence along West Florissant had been begun to diminish.

At the protest a day earlier, tensions escalated after several hundred people gathered in the street, ignoring repeated warnings to get to the sidewalk or face arrest. Then, several gunshots suddenly rang out from an area near a strip of stores, including some that had been looted moments earlier. The shots sent protesters and reporters running for cover.

Belmar said he believed there were six shooters, including 18-year-old Tyrone Harris Jr., who Belmar said then opened fire on officers.

Police had been watching Harris during the protest out of concern that he was armed, the chief said.

During the gunfire, Harris crossed the street and apparently spotted plainclothes officers arriving in an unmarked van with distinctive red and blue police lights, Belmar said. The suspect allegedly shot into the windshield of the van.

The four officers in the van fired back, then pursued the suspect on foot. The suspect again fired on the officers when he became trapped in a fenced-in area, the chief said, and all four opened fire.

Harris was in critical condition after surgery. Prosecutors announced 10 charges against him — five counts of armed criminal action, four counts of first-degree assault on a law enforcement officer and a firearms charge. All 10 are felonies.

All four officers in the van, each wearing protective vests, escaped injury. They were not wearing body cameras, Belmar said.

Harris’ father called the police version of events "a bunch of lies." He said two girls who were with his son told him he was unarmed and had been drawn into a dispute involving two groups of young people.

Tyrone Harris Sr. told The Associated Press that his son was a close friend of Michael Brown and was in Ferguson on Sunday night to pay respects.

The elder Harris said his son got caught up in a dispute among two groups of young people and was "running for his life" after gunfire broke out.

"My son was running to the police to ask for help, and he was shot," he said. "It’s all a bunch of lies … They’re making my son look like a criminal."

Online court records show that Tyrone Harris Jr. was charged in November with stealing a motor vehicle and a gun, as well as resisting arrest by fleeing. A court hearing in that case is scheduled for Aug. 31.

Belmar said the suspect who fired on officers had a semi-automatic 9 mm gun that was stolen last year from Cape Girardeau, Missouri.

The police chief drew a distinction between the shooters and the protesters.

"They were criminals," he said of those involved in gunfire. "They weren’t protesters."

Gov. Jay Nixon agreed, saying in a statement that such "reprehensible acts must not be allowed to silence the voices of peace and progress."

Associated Press reporter Alan Scher Zagier and photographer Jeff Roberson contributed to this report.