Police in Baltimore fired smoke bombs and pepper pellets at hundreds of protesters who defied a night-time curfew that took effect across the city late Tuesday, police and US media said.

"Officers are now deploying pepper balls at the aggressive crowd at North Ave/Pennsylvania Ave," police tweeted, while CNN and other television news stations said that officers also used smoke bombs in a bid to enforce a 10:00 pm (0200 GMT Wednesday) curfew.