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FERGUSON, Missouri — An almost festive atmosphere descended a St. Louis suburb on Thursday night as tensions cooled dramatically after policing was transferred to state troopers in the wake of four days of unrest over the shooting death of unarmed teenager Michael Brown.

Few law enforcement officers were visible late Thursday on the streets of Ferguson, Missouri, as hundreds of people thronged the streets and drivers honked horns in celebration after Gov. Jay Nixon ordered the state Highway Patrol to take over security. In front of the McDonald's restaurant that had been a flashpoint of confrontation Wednesday, an African-American man chatted amiably with two uniformed officers who weren't wearing tactical gear — unlike the military-style appearance of Ferguson police earlier in the week.

Nixon put Highway Patrol Capt. Ron Johnson, who is African-American and grew up in Ferguson, in charge of troopers policing the city. Cheers greeted him when he grabbed a megaphone Thursday afternoon and told the crowd that he and his officers were "going to march with you."

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"There will be no police line," he promised.

Johnson led a peaceful march through town, hugging residents and shaking hands along the way.

Missouri Highway Patrol Capt. Ron Johnson hugs Angela Whitman in Ferguson, Missouri, after he was assigned responsibility for security on Thursday. David Carson / St. Louis Post-Dispatch via AP

"So far, so good," said a trooper who wouldn't give his name because officers weren't supposed to talk to the media. "It's been a mixed reception, but lots of positive."

There was a brief flare-up when a group marched up the street and surrounded those two state police cars, demanding to know the identity of the officer who shot Brown on Saturday. "What's his name?" they chanted — but they dispersed peacefully when the police drove away.

"People feel less intimidated, less threatened," Vernon Jackson of Ferguson told NBC News. "It's generated a different result, more positivity, unity."

Earlier, Johnson told reporters: "I understand the anger and fear the residents of Ferguson are feeling, and our police officers will respect both of them. It means a lot to me personally that we break this cycle of violence."

President Barack Obama also appealed Thursday for "peace and calm" in Ferguson and called for restraint by all involved.

- M. Alex Johnson and Rick Brown