Baltimore police have arrested about 34 people and six officers were hurt when protests over the death in custody of a young black man turned violent.

"A small contingent of yesterday's protesters caused violent disruptions downtown and in west Baltimore last night and early this morning after what had been mostly peaceful protests throughout the day," Baltimore police spokesman Jeremy Silbert said.

"Approximately 34 people were arrested and six officers suffered minor injuries."

Freddie Gray, 25, died a week ago from a severe spinal injury following his arrest, triggering demonstrations that escalated on Saturday and saw protesters rampage through downtown Baltimore, which is less than an hour from the US capital Washington.

"Multiple storefronts were vandalised and several police vehicles and other property was damaged," the spokesman said in a statement.

"Members of the BPD (police) along with our local and state law enforcement partners worked through the early morning hours to calm the situation."

He added: "We will continue to have extra officers deployed throughout the city this weekend."