The US National Guard have been called in to Baltimore after a state of emergency was declared as protesters clash with police.
In the latest display of unrest following the death of a black man who was injured while in police custody, footage showed protesters confronting officers wearing full riot gear.
Maryland Governor Larry Hogan’s office announced he had signed an order declaring a state of emergency and activated the National Guard to halt the violence.
Baltimore police said at least seven officers were injured after a group of juveniles began throwing “bricks, rocks and other items” at police.
The group “attacked officers without provocation”, Captain Eric Kowalczyk said.
He said officers suffered “broken bones and one officer is unresponsive”.
Newly sworn-in US Attorney General Loretta Lynch – just hours into her job – briefed President Barack Obama, the White House said.
The President also spoke to Baltimore Mayor Stephanie Rawlings-Blake about the violence.
The city’s Major League Baseball team, the Orioles, postponed their home game against the Chicago White Sox after consulting with police.
Earlier on Monday, the Baltimore Police Department said it had received a “credible threat” that various gangs had agreed to work together to “take out” police officers.
The clashes began just hours after mourners gathered for the funeral of Freddie Gray, who died in hospital a week after suffering a spinal injury while in police custody.
His death on 19 April has been followed by a week of mostly peaceful protests across the city.
Events turned ugly on Saturday night, however, when demonstrators began smashing shop windows, looting merchandise and vandalising police cars.
On Monday, several people were seen smashing another police vehicle. An armoured truck carrying officers arrived a short time later sending the rioters scattering.
Additional footage later showed other cars engulfed in flames.
Officers were “using fire extinguishers to put out small fires in the area”, the police department posted on Twitter.
Several shops, including a cheque-cashing store and a CVS pharmacy were looted, police said.
“Several juveniles are part of these aggressive groups. We are asking all parents to locate their children and bring them home,” the department said in another Twitter post.
The clashes occurred in west Baltimore, not far from where Mr Gray was taken into custody on 12 April for carrying a knife.
His death has fuelled the growing national debate on the use of police tactics, particularly in regard to the treatment of young black men.
Similar incidents resulting in the deaths of black men in Ferguson, Missouri, New York City, Cleveland and South Carolina have also led to calls for changes in policing.
Six Baltimore police officers have been suspended pending an internal investigation into Mr Gray’s death.
The city’s police commissioner said officers failed to provide Mr Gray with timely medical attention for the injury after he was put inside a police van.
Authorities are also investigating why he was not fastened with a seat belt for the ride to the station.