Armed National Guard troopers in battledress deployed in force in Baltimore on Tuesday after a riot triggered by anger over the death of an African American arrested by police.
Thousands of military and police reinforcements have been ordered to the US port city to quell unrest in which cars were torched, stores looted and officers attacked.
Maryland Governor Larry Hogan was on the street as dawn rose, inspecting a National Guard barricade and vowing to "make sure what happened last night in Baltimore City is not going to happen again."
"This violence is not going to be tolerated," he told reporters at the temporary checkpoint, manned by riot police and Guard troopers with assault rifles.
"By tonight you're going to see an overwhelming display of people out there on the streets protecting the citizens," he vowed, in a nod to criticism that authorities were slow to act.
Baltimore has declared an overnight curfew from 10:00 pm Tuesday (0200 GMT Wednesday) and local and national leaders have appealed for calm after the latest in a series of incidents to stir US racial tension.
Rioting erupted Monday after the funeral of Freddie Gray, a 25-year-old Baltimore man who died of severe spinal injuries eight days after he was detained by city police.
An investigation has been launched into the cause of his injuries, but many local people see the incident as only the latest example of police brutality against black suspects.
Gray's family and local community leaders appealed for calm, but tempers boiled over as young, mainly African American men pelted police with stones and looted businesses.
At least 15 police officers were injured overnight, two of them seriously, and at least 200 suspects were arrested, according to US media, citing city authorities.
As volunteer clean-up teams took to the streets Tuesday, residents spoke of their terror as gangs roamed the streets fighting police and destroying property.
- Civil rights struggle -
"It was horrific to the point where my children were actually crying trying to get back to the house because there was so much going on," Latania Graham told AFP.
"I just feel like my ancestors have fought for things to be calmer than this. They already did the work for us, and to be still going through this almost 50 years later is unbelievable to me," she said, referring to the African American civil rights struggle.
Baltimore schools were closed on Tuesday as a safety measure, although some residents worried that this would lead to more restless teenagers on the tense streets.
Police urged parents to control their children and news footage showed one mother slapping her son in the head and screaming at him for taking part in the unrest.
The Baltimore Sun, quoting police, reported two people injured in separate shootings. Police confirmed they were investigating after a woman was shot in the leg.
The violence is the latest in a series of confrontations between US police and mainly young African American men enraged by what they see as racist attitudes.
Last summer's fatal shooting of unarmed teenager Michael Brown by a white police officer in Ferguson, Missouri triggered coast-to-coast protests.
Maryland police superintendent Colonel William Pallozzi said he had ordered 500 police into the city and requested 5,000 more from the wider Mid-Atlantic region.
National Guard commander Adjutant General Linda Singh said she had 5,000 troopers ready and would deploy them in "massive force" to protect people and property.
President Barack Obama was briefed late Monday on the rapidly evolving situation by Baltimore Mayor Stephanie Rawlings-Blake and his new Attorney General Loretta Lynch.
On Monday, thousands of mourners gathered for Gray's funeral in New Shiloh Baptist church in the city's impoverished Sandtown neighborhood.
Before the service, a cryptic message circulated on social media called for an after-school "purge," street slang for random acts of lawlessness.
- Spinal injuries -
Lawyers for Gray's family say his death, after a week in a coma, was caused by severe spinal injuries sustained following his arrest.
Six officers have been suspended with pay pending the outcome of a police investigation that is to be submitted to state prosecutors by Friday.
Police confirmed Gray had requested medical help and an inhaler after he was detained and have acknowledged he should have received medical attention sooner.
In video taken by bystanders, Grey can be heard howling in pain as his limp body is dragged into the van during his arrest.