Baltimore streets once filled with rock- and bottle-throwing protesters are quiet and nearly empty of civilians as residents heed an overnight curfew enforced by 3,000 police and National Guardsmen.

The curfew, in effect from 10 p.m. Tuesday to 5 a.m. Wednesday, got off to a rocky start, when as many as 200 protesters showed no immediate signs of going home.

A line of police behind riot shields hurled tear gas canisters and fired pepper balls at the stragglers to enforce the curfew, which was imposed to prevent a repeat of Monday's riots, the worst in Baltimore since 1968.

Demonstrators threw bottles at police, and picked up the canisters and hurled them back at officers. No immediate arrests or serious injuries were reported, and the crowd rapidly dispersed. It was down to just a few dozen people within minutes.