Scores of demonstrators had remained in the streets after the curfew took effect at midnight (0500 GMT). Law enforcement officials used loudspeakers to warn protesters to disperse immediately. Officers, equipped with gas masks and full-length shields, stood among and on top of armored vehicles.
Governor Jay Nixon declared a state of emergency and announced the five-hour curfew after a week of racially charged protests and looting over the shooting of 18-year-old Michael Brown by Ferguson police officer Darren Wilson, 28, in the suburban St. Louis community in the Midwest US state on Aug. 9.
Missouri State Highway Patrol Captain Ron Johnson said the person shot at a restaurant was in critical condition. Police were unable to identify the victim, who he said was not shot by police, and that the alleged shooter was still at large.
Seven people were also arrested for failing to disperse after the curfew took effect, Reuters reported.
Johnson said canisters of smoke and later teargas were fired as part of police attempts to reach the victim of the restaurant shooting, "and not in relation to the curfew." The shooting victim was taken to hospital by bystanders before police could reach him.
Johnson also said someone had shot at a passing police car but was not apprehended, adding "I was disappointed in the actions of tonight," noting "the crowds we've had for the last two nights (were) citizens obeying, protesting."
The smoke and teargas canisters largely dispersed the crowd, some of whom had been chanting "No justice, no curfew, no peace", while others implored the crowd not to move forward towards police.
On Saturday evening the mood among the protesters on a main road in Ferguson had been tense and defiant following days of demonstrations and some looting.