Commissioner Anthony Batts announced the measure in a press conference, according to the Associated Press.
Batts added the city expected large marches during the coming weekend. He did not say when law enforcement officials would lift restrictions on city residents.
Baltimore police first imposed a curfew Tuesday night. In effect from 10 p.m. to 5 a.m., it was originally supposed to end Friday.
The ban was in response to violent riots that gripped the city Monday.
Authorities said Tuesday they had arrested 235 people for looting, vandalism and other crimes related to the chaos.
Fury erupted last weekend over the death of Freddie Gray, 25, on April 19. Gray, who was black, died after a fatal spinal injury suffered while in police custody.
The incident has sparked national debate over the relationship between law enforcement and the minority communities they protect.
Similar demonstrations have taken place in Philadelphia, New York and other cities across the country.