A curfew has been declared in the US city of Baltimore amid violent protests over the death of a black man fatally injured in police custody.
After dark, live video from helicopters showed several buildings in central Baltimore on fire.
Earlier, dozens of people were seen confronting police, and 15 officers were injured.
The governor of Maryland declared a state of emergency, calling in the national guard as clashes intensified.
African American Freddie Gray, 25, died on 19 April after a week in a coma. Where and when his injuries were sustained is being investigated by the justice department.
Officials have suspended six police officers who were involved in the case.
Monday’s clashes began hours after Gray’s funeral.
Baltimore Mayor Stephanie Rawlings-Blake said it was very clear there was a difference between the “peaceful protests of those who seek justice” and the “thugs who want to incite violence”.
She said: “We are deploying every resource possible to regain control of the situation.”
She has ordered a week-long curfew from 22:00 to 05:00 starting on Tuesday.
Earlier, President Barack Obama said his administration would provide her assistance as needed.
Governor Larry Hogan issued an executive order to “protect the lives and property of citizens being impacted by this public emergency”.
Capt Eric Kowalczyk of Baltimore Police said the 15 injured officers were wounded by thrown objects including bricks and bottles.
Two remain in hospital.
Associated Press reported two dozen people had been arrested.
Before nightfall, scenes included a blaze at a CVS pharmacy, the looting of stores and the burning and vandalism of law enforcement vehicles.
Baltimore’s Major League Baseball team the Orioles cancelled Monday night’s game against Chicago’s White Sox as a result of the violence.
Freddie Gray’s death is the latest in a string of high-profile cases where black men have died after contact with the police.
Nationwide protests followed the killing of unarmed black teenager Michael Brown by a white police officer in Ferguson, Missouri, last year.
Baltimore officials likened Monday’s violence to scenes witnessed after the 1968assassination of black civil rights leader Dr Martin Luther King and said the city had taken a long time to recover from it, urging calm.
Earlier in the day, 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 had entered into a partnership” to target officers.
The violence is an escalation of earlier protests over the weekend that turned violent.
There were 34 arrests as peaceful demonstrations by about 1,200 people outside City Hall on Saturday afternoon got out of control.
Six police officers sustained minor injuries in that episode.