Missouri state police are taking over security from local officers in the St Louis suburb that has been the scene of violent protests since an unarmed black teenager was shot dead by white police officer.
President Barack Obama has appealed for "peace and calm" on the streets of Ferguson, the predominantly black city where crowds have gathered to protest since Saturday's shooting of 18-year-old Michael Brown.
Governor Jay Nixon announced that state highway patrol captain Ron Johnson, who is black, will take over security after the local police response drew heavy criticism.
Mr Nixon said the change was intended to make sure "that we allow peaceful and appropriate protests, that we use force only when necessary, that we step back a little bit and let some of the energy be felt in this region appropriately".
His promise to ease the deep racial tensions was swiftly put to the test as demonstrators gathered again last night in the neighbourhood where looters smashed and burned businesses on Sunday and police repeatedly fired tear gas and smoke bombs.
Capt Johnson said he grew up in the community and "it means a lot to me personally that we break this cycle of violence". He said he planned to keep heavily armoured vehicles away from the scene and told his officers not to bring tear gas masks.
Highway patrol captain Ron Johnson is leading protesters on a march through Ferguson. A corner turned? pic.twitter.com/ewytjhz2uP— Jon Swaine (@jonswaine) August 14, 2014
By late afternoon, Capt Johnson was walking down the street with a group of more than 1,000 protesters as they chanted "Hands up, don't shoot", a reference to witness accounts that described Mr Brown as having his hands in the air when the officer kept firing.
Capt Johnson planned to talk to the demonstrators throughout the night. "We're going to have some conversations with them and get an understanding of what's going on," he said.
Mr Obama, speaking from the Massachusetts island where he is on a two-week holiday, said there was no excuse for excessive force by police in the aftermath of the shooting and he had asked the Justice Department and FBI to investigate the incident.
"I know emotions are raw right now in Ferguson, and there are certainly passionate differences about what has happened," he said.
"But let's remember that we're all part of one American family. We are united in common values, and that includes the belief in equality under the law, respect for public order and the right to peaceful public protests."
St Louis County police spokesman Brian Schellman said officers used tear gas on Wednesday night to disperse a large crowd of protesters after some threw Molotov cocktails and rocks at officers. More than 10 people were arrested in Ferguson.
Residents have complained about the police response that began soon after Mr Brown's shooting with the use of dogs for crowd control - a tactic that for some evoked civil-rights protests from a half-century ago.
The county police force took over, leading both the investigation of the shooting and the subsequent attempts to keep the peace at the smaller city's request.
County police chief Jon Belmar said his officers responded with "an incredible amount of restraint" as they had rocks and bottles thrown at them, were shot at and had two dozen patrol vehicles destroyed.
The city and county are also under fire for refusing to release the name of the officer who shot Mr Brown, citing threats against him and others. Hacker group Anonymous yesterday released a name purported to be that of the officer, but the police chief later said the name was incorrect.
Twitter quickly suspended the Anonymous account that posted the officer's alleged identity and personal information. The site's code of conduct strictly forbids the publication of private and confidential information without permission.
Police have said Mr Brown was shot after an officer encountered him and another man on the street.
They say one of the men pushed the officer into his squad car, then physically assaulted him in the vehicle and struggled with the officer over the officer's weapon. At least one shot was fired inside the car.
The struggle then spilled on to the street, where Mr Brown was shot multiple times.
The officer involved was injured, with one side of his face swollen, Ferguson police chief Thomas Jackson said.
Dorian Johnson, who says he was with Mr Brown when the shooting happened, told a much different story.
He said the officer ordered them out of the street, then grabbed his friend's neck and tried to pull him into the car before brandishing his weapon and firing. He said Mr Brown started to run and the officer pursued him, firing several times.
Mr Johnson and another witness both say Mr Brown was on the street with his hands raised when the officer fired at him repeatedly.
US attorney general Eric Holder has said federal investigators have interviewed eyewitnesses and a person familiar with the matter said federal authorities had interviewed Mr Johnson.
Mr Holder spoke by telephone with Mr Brown's family yesterday to offer condolences and to tell them that the Justice Department was committed to a full and independent investigation.