WASHINGTON, April 27 (Xinhua) -- Thousands of U.S. National Guard soldiers and police forces began mobilizing Monday evening toward Baltimore, Maryland, after Governor Larry Hogan declared a state of emergency in response to escalating violence.

The unrest in Baltimore City erupted following the funeral of a 25-year-old black man who died after being injured in police custody.

"Today's looting and acts of violence in Baltimore will not be tolerated," said Hogan in a statement issued late Monday.

"There is a significant difference between protesting and violence and those committing these acts will be prosecuted under the fullest extent of the law," he said.

According to Baltimore Police Department, currently around 1,500 police officers were deployed to stem the unrest as hundreds of men and women were setting fire to cars, looting stores and throwing bricks at police.

It was estimated that apart from the 5,000 deployed National Guard troops, another 5,000 police forces across the region would be needed.

"I have not made this decision lightly," said Hogan late Monday evening in a televised news conference. "The National Guard represents that last resort to restore order."

Hundreds of rioters in northwest Baltimore Monday afternoon looted stores and went into confrontation with police force with bricks, hours after the funeral of Freddie Gray, who passed away on April 19 after being severely injured a week earlier during police arrest.

Well before the funeral rituals ended, Baltimore police announced a "credible threat," saying that three violent gangs were believed to have entered into a "partnership" to target law enforcement officers.

A CVS pharmacy store in the worst-affected area was set ablaze after being looted on Monday evening, and several cars, including at least three police patrol cars, were set on fire.

As looters continued to "break into business and set cars on fire," as declared by the police department on its twitter account, Baltimore Mayor Stephanie Rawlings-Blake announced curfew Monday evening.

"A general curfew will be in effect in Baltimore City from 10 p.m. April 28 to 5 a.m. May 4, unless renewed or rescinded by order of the Mayor," said the Baltimore Police Department in an online statement.

At least 27 people had been arrested by Monday evening. According to Baltimore Police Department, 15 police officers were injured during conflicts with rioters.

Meanwhile, newly sworn-in U.S. Attorney General Loretta Lynch on Monday condemned the rioting, calling for the Baltimore community to "adhere to the principles of nonviolence" as the Justice Department was launching an investigation into the Gray case.

In a statement issued on her first day as the 83rd U.S. Attorney General, Lynch said those who participated in looting and smashing "ostensibly in protest" of the death of Gray had done a "disservice to Gray's family."

"I condemn the senseless acts of violence by some individuals in Baltimore that have resulted in harm to law enforcement officers, destruction of property and a shattering of the peace in the city of Baltimore," said the statement.

Lynch said the Justice Department had already joined efforts with FBI to launch an independent criminal civil rights investigation into Gray's death, adding that her department had also started its review of the Baltimore City Police Department.

Preliminary investigation indicated that Gray had suffered a severe spinal injury during or shortly after his arrest, and Baltimore's Police Commissioner Anthony Batts acknowledged on Friday that Gray was not treated properly after being arrested.

Police brutality in the Gray case thrusted Baltimore into the epicenter of a nationwide debate over racial relations following a spate of deaths of unarmed black men caused by white police officers.

"We can imbue our criminal justice system with both strength and fairness, for the protection of both the needs of victims and the rights of all," said Lynch earlier on Monday during her swearing-in ceremony at the Justice Department. "We can restore trust and faith both in our laws and in those of us who enforce them."

So far, no officers involved in Gray's death have been charged and few details about Gray's arrest was released.