Seven police officers in Baltimore have been injured and one is "unresponsive" after protests there turned violent.
Live video from helicopters shows dozens of people in the streets, confronting officers and smashing at least one police car.
Captain Eric Kowalczyk said police were attempting to take control of the situation and would deploy tear gas and "pepper balls".
Protests have taken place since the death of Freddie Gray on 19 April.
Mr Gray, 25, died after an encounter with police a week earlier during which he sustained serious and unexplained spinal injuries.
The protests and clashes come just hours after Mr Gray's funeral.
The violence "does not reflect the spirit of this movement", Pastor Jamal Bryant, an organiser of protests in previous days, said on US television.
He said members of his church were going into the area to make appeals to the protestors to go home.
"These are not protestors - these are lawless individuals," Mr Kowalczyk told CNN.
Video showed looters ransacking a neighbourhood market, and, in a separate incident, burning a law enforcement vehicle. Separately, protestors destroyed a police car by jumping on it and smashing the windows.
Officials said the protestors threw bricks, rocks and other items at police officers.
Earlier today, a statement released by police said that its Criminal Intelligence Unit learned "that members of various gangs including the Black Guerrilla Family, Bloods, and Crips have entered into a partnership" to target officers.
The violence is an escalation of earlier protests during the weekend which turned violent.
There were 34 arrests as peaceful demonstrations by about 1200 people outside City Hall on Saturday afternoon got out of control.
Six police officers sustained minor injuries in that episode.