The latest confrontation occurred when demonstrators remained in the streets of the St Louis suburb after the curfew took effect at midnight. Seven people were arrested for failing to disperse, police said.
A person was shot and critically wounded during the night. It was not clear why, and the shooter was still at large, police said.
Missouri governor Jay Nixon imposed the curfew on Saturday after a week of racially charged protests and looting over the August 9 shooting of 18-year-old Michael Brown by Ferguson police officer Darren Wilson.
The Ferguson police department has come under strong criticism for both the shooting and its handling of its aftermath.
On Sunday US Attorney General Eric Holder ordered a federal medical examiner to perform an autopsy, in addition to one being conducted by state medical examiners.
Holder called for the federal autopsy “due to the extraordinary circumstances involved in this case and at the request of the Brown family”.
The family is also planning to have a pathologist conduct an independent examination of the body, a family spokesman said.
Unrest in Ferguson flared anew on Friday after the local police released a video showing the alleged participation by Brown in a convenience store robbery shortly before the fatal shooting.
Police have said the officer who shot Brown had no idea he was a robbery suspect.
The Missouri governor slammed the decision to release the video. “I think it had an incendiary effect,” Nixon said, adding that police “clearly are attempting to besmirch a victim of a shooting”.
As the curfew took effect on Saturday night, law enforcement officials used loudspeakers to tell protesters to disperse.
Officers, equipped with gas masks and full-length shields, stood among and on top of armoured vehicles.
The person shot at a restaurant during the night was in critical condition, but was not shot by police.
Missouri State Highway Patrol Captain Ron Johnson said teargas was fired as part of police attempts to reach the victim of the shooting.
The governor said he did not know how long the curfew would be in place.
Civil rights activist Al Sharpton, who was set to lead a rally with the dead teen’s family yesterday in Ferguson, called for an end to violence and looting.
“We cannot change it by becoming like those that we fight,” he said.