Police fired smoke and tear gas canisters early Sunday in an effort to disperse several dozen protesters who defied a curfew in a St. Louis suburb where a black teenager was fatally shot by a white police officer last week.

The Missouri Highway Patrol said that seven people were arrested and one man had been shot at the site of the protest in Ferguson, Mo. Missouri State Highway Patrol Capt. Ron Johnson said that the shooting victim was in critical condition and had been rushed to a hospital by protesters.

Johnson said the use of tear gas was precipitated by concerns about people who'd broken into a barbecue restaurant and taken position on the roof overlooking approaching police. Another concern involved a man flashing a handgun who appeared in the middle of the street as armored vehicles approached. Johnson says someone fired at a patrol car, but no officers were injured.

"I was disappointed in the actions of tonight," Johnson said.

The St. Louis Post-Dispatch reported that St. Louis Alderman Antonio French, who has taken part in demonstrations all week, told reporters that the police's tactics "were a lot better" than they could have been. French also said that he had attempted to convince people to honor the curfew, but some "didn't want to be told to leave."

French later tweeted, "I can tell you firsthand that some of the people that remained tonight were armed. Were ready for a fight. And wanted to injure police."

Hundreds of other protesters had left peacefully before the midnight-to-5 a.m. curfew took effect, but remaining protesters -- chanting "No justice! No curfew!" -- refused to leave the area.

As five armored tactical vehicles approached the crowd, officers spoke through a loudspeaker: "You are in violation of a state-imposed curfew. You must disperse immediately. Failure to comply may result in arrest."

Highway Patrol Spokesman Lt. John Hotz initially said police only used smoke, but later told The Associated Press that they also fired tear gas canisters. He said of police efforts: "Obviously, we're trying to give them every opportunity to comply with the curfew."

As officers put on gas masks, a chant from the distant crowd emerged: "We have the right to assemble peacefully." A moment later, police began firing canisters into the crowd. Protesters said their faces and eyes had been burned. Others screamed in pain.

Jayson Ross, who was leading the protesters toward police, said: "They got guns. We got guns. We are ready."

The curfew had been announced by Missouri Gov. Jay Nixon Saturday afternoon in an effort to prevent the violence and looting that had marred earlier protests over the August 9 death of 18-year-old Michael Brown. The governor also declared a state of emergency.

Early Sunday, Johnson said that authorities were not aware of any looting that had occurred during the night.

Stormy weather and the urgings of protest leaders made the decision to go home before midnight easier for some. As midnight approached late Saturday, New Black Panther Party leader Malik Shabazz roamed the street with a bullhorn, encouraging people to leave for their own safety.

"C'mon you all, let's roll out," Shabazz said through his bullhorn. "Let's roll out of here, get some rest and come back tomorrow."

Nixon said Sunday morning on ABC's "This Week" that he was not aware the police were going to release the surveillance video.

"It's appeared to cast aspersions on a young man that was gunned down in the street. It made emotions raw," he said.

In announcing the curfew, Nixon said that though many protesters were making themselves heard peacefully, the state would not allow looters to endanger the community.

"I am committed to making sure the forces of peace and justice prevail," Nixon said during a Saturday press conference at a church that was interrupted repeatedly by people objecting to the curfew and demanding that the officer who shot Brown be charged with murder.

"We must first have and maintain peace. This is a test. The eyes of the world are watching," Nixon said. "We cannot allow the ill will of the few to undermine the good will of the many."

Nixon's curfew announcement came after tensions again flared in Ferguson late Friday night. Earlier that day, local police identified the officer who shot Brown as Darren Wilson and released documents and video footage alleging that Brown had robbed a convenience store just before he was shot. Police said Wilson was unaware Brown was a suspect when he encountered him walking in the street with a friend.

Law enforcement officials tell Fox News that the footage of Brown in the convenience store was released by local authorities over the Justice Department's objections. One official told Fox News that federal authorities had their own copy of the tape and did not intend to make it public.

In a statement Sunday, Justice Department spokesman Brian Fallon said Attorney General Eric Holder has requested an additional autopsy of Brown to be performed by a federal medical examiner.

"This independent examination will take place as soon as possible," the statement said. "Even after it is complete, Justice Department officials still plan to take the state-performed autopsy into account in the course of their investigation."

Johnson, who is in charge of security in Ferguson, said 40 FBI agents were going door-to-door in the neighborhood starting Saturday, talking to people who might have seen or have information about the shooting.

Johnson assured those at the news conference that police would not enforce the curfew with armored trucks and tear gas but would communicate with protesters and give them ample opportunity to leave. Nixon and Johnson were flanked by numerous local elected officials, including U.S. Rep. William Lacy Clay Jr., who urged Johnson to be flexible with the midnight curfew.

But they were interrupted repeatedly.

"Why is the focus on security and not getting justice? Why is there not an arrest?" one women yelled.

Brown's death had already ignited several days of clashes with furious protesters. Tensions eased Thursday after Nixon turned oversight of the protests over to the Missouri Highway Patrol. Gone were the police in riot gear and armored vehicles, replaced by the new patrol commander who personally walked through the streets with demonstrators. But Friday night marked a resurgence of unrest.

On Saturday, some residents said it appeared the violent acts were being committed by people who came from other suburbs or states.

"Who would burn down their own backyard?" asked Rebecca McCloud, a local who works with the Sunshine Baptist Church in St. Louis. "These people aren't from here. They came to burn down our city and leave."

Local officers faced strong criticism earlier in the week for their use of tear gas and rubber bullets against protesters. Johnson said one tear gas canister was deployed Friday night after the group of rioters became unruly and several officers got trapped and injured.

Wilson, the officer who shot Brown, is a six-year police veteran who had no previous complaints against him, the local police chief has said.

The Ferguson Police Department has refused to say anything about Wilson's whereabouts, and Associated Press reporters were unable to contact him at any addresses or phone numbers listed under that name in the St. Louis area.

Wilson has been on paid administrative leave since the shooting. St. Louis County prosecutor Bob McCulloch said it could be weeks before the investigation wraps up.

Fox News' Jake Gibson and The Associated Press contributed to this report.

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