By Ellen Wulfhorst
FERGUSON, Missouri, Aug 18 (Reuters) - Gunfire was heard and police used tear gas and smoke canisters to disperse protesters as chaos erupted Sunday night in Ferguson, Missouri, which has been racked by protests since an unarmed black teenager was shot by police last week.
Hundreds of protesters, including young children, fled to safety after police wearing gas masks and body armor fired canisters of smoke to disperse them hours ahead of a planned midnight curfew. The Missouri Highway Patrol said some tear gas was used along with the smoke bombs.
Gunfire was heard, by a Reuters reporter and photographer, but it was unclear where it was coming from.
A crowd of about 400 appeared to be marching peacefully, and included numerous families with children, when police used smoke canisters to disperse them.
"The smoke bombs were completely unprovoked," said Anthony Ellis, 45. "It (the protest) was led by kids on bikes. Next you know, they're saying, 'Go home, Go home!'
The Missouri Highway Patrol said "aggressors" were trying to infiltrate a law enforcement command post and that armored vehicles were deployed to ensure public safety.
"We ordered them back. We ordered them back again. After several attempts, we utilized the smoke to disperse these individuals," said Missouri Highway Patrol Corporal Justin Wheetley.
He later said that at least one Molotov cocktail had been thrown at police, although some witnesses said those were tear gas canisters being thrown back at police.
The police action, which involved heavily armed officers and armored vehicles, took place hours before a midnight curfew imposed for the second night in the tense St. Louis suburb, site of ongoing protests as well as violence and looting since Michael Brown, 18, was shot to death on Aug. 9.
Earlier on Sunday, U.S. Attorney General Eric Holder ordered a federal autopsy of Brown's body, seeking to assure the family and community there will be a thorough investigation into a death that has sparked days of racially charged protests.
Brown was shot by white police officer Darren Wilson.
Police say Brown was asked by Wilson to move out of the road and onto a sidewalk and that Brown reached into a patrol car and struggled with Wilson for his service gun and was shot.
A friend of Brown's, Dorian Johnson, 22, and at least one other witness said Wilson reached out through his car window to grab at Brown and the teenager was trying to get away when shot. Brown held up his hands in a sign of surrender, but Wilson got out of his patrol car and shot Brown several times, they said.
A preliminary private autopsy, asked for by Brown's family, shows the teenager was shot at least six times, the New York Times reported on Sunday night.
Citing Dr. Michael M. Baden, former chief medical examiner for the City of New York, the newspaper reported that Brown was shot twice in the head, and that the bullets that hit him did not appear to have been fired from very close range because no gunpowder was detected on his body.
That conclusion could change, however, if gunshot residue is found on Brown's clothing, the newspaper said.
The police department in the St. Louis suburb has come under strong criticism for Brown's death and its handling of the aftermath. The clashes in Ferguson have pitted mostly black protesters against mostly white police in a residential and retail district.
The Highway Patrol captain charged with restoring order told hundreds of people at a local church for a rally on Sunday that he was committed to protecting their right to protest.
"I'm sorry," Captain Ron Johnson, who is black, told Brown's family during remarks that prompted repeated standing ovations at the rally. "My heart is heavy."
The mood at the rally was somber, as a choir sang gospel music at Greater Grace Church, civil rights activist the Rev. Al Sharpton asked participants to join hands and prepare themselves for difficult days ahead as the results of three autopsies of Brown's body become public, and his funeral is held.
"This is a defining moment in this country," Sharpton told the crowd. Brown's death "will change this town," he said.
In St. Louis on Sunday, about 125 people attended a rally in support of officer Darren Wilson, the St. Louis Metropolitan Police Department said. Protesters held signs that read, "We love and support you Darren" and "Support our police. Pray for peace."
On Saturday, police also used smoke canisters and tear gas to disperse protesters who refused to leave the area when the midnight-to-5 a.m. curfew began. Seven protesters were arrested after failing to disperse.
Overnight Saturday, one person was shot and critically wounded. The circumstances were not clear, and the shooter was still at large, police said. Johnson said police were unable to identify the victim, who he said was not shot by police.
Missouri Governor Jay Nixon, a Democrat, criticized the Ferguson police department for releasing a video on Friday purporting to show Brown taking part in a convenience store robbery shortly before the shooting. Police have said the officer who shot Brown had no idea he was a robbery suspect.
"I think it had an incendiary effect," Nixon said on CBS' "Face the Nation." Police "clearly are attempting to besmirch a victim of a shooting," he added.
At Sunday's rally at the church, some participants referred to the theft of a box of cigars as shoplifting; police had initially called it a strong-arm robbery.
Ferguson Police Chief Tom Jackson defended the release of the surveillance video over the objections of the U.S. Justice Department. Jackson said he was complying with the news media's requests for information in the case.
The decision to release the video while not giving details of the shooting only fueled outrage. (Additional reporting by Lucia Mutikani, and Julia Edwards in Washington, Victoria Cavaliere in Seattle and Dana Feldman in Los Angeles; Writing by Colleen Jenkins and Sharon Bernstein; Editing by Frances Kerry, Cynthia Osterman; Eric Walsh and Michael Perry)