National Guard troops and police in riot gear patrolled Baltimore to enforce a curfew, dispersing protesters with tear gas, pepper spray and rubber bullets.

With helicopters overhead and armoured vehicles on the ground, most people respected a curfew that starts at 10pm and goes until 5am all week. However, a few hundred people defied authorities, gathering at an intersection that was the scene of rioting a night earlier.

Baltimore Freddie Gray
Police form a line at North Ave and Pennsylvania Ave in Baltimore, on April 28, 2015Eric Thayer/Reuters
Baltimore Freddie Gray
A demonstrator stands in front of the police line on the corner of West North Avenue and Pennsylvania Avenue, on April 28, 2015Shannon Stapleton/Reuters
Baltimore Freddie Gray
April 28, 2015: A helicopter with a spotlight hovers over police and protesters near the CVS pharmacy that was set on fire, before the introduction of a mandatory, city-wide curfew of 10pmAndrew Burton/Getty Images
Baltimore Freddie Gray
Protesters defy the curfew in front of a line of police officers on April 28, 2015, the night after city-wide riotingMark Makela/Getty Images
Baltimore Freddie Gray
Protesters gesture at police shortly before the deadline for a city-wide curfew passed in Baltimore, on April 28, 2015Eric Thayer/Reuters
Baltimore Freddie Gray
A police line blocks the street as clouds of smoke rise shortly after the deadline for a city-wide curfew passed in Baltimore, on April 28, 2015Shannon Stapleton/Reuters
Baltimore Freddie Gray
A protester throws a gas canister back at police during clashes at North Ave and Pennsylvania Ave in Baltimore, on April 28, 2015Eric Thayer/Reuters
Baltimore Freddie Gray
April 28, 2015: A protester carrying a sign walks through tear gas near the CVS pharmacy that was set on fire as police enforce a mandatory, city-wide curfew of 10pmAndrew Burton/Getty Images
Baltimore Freddie Gray
An armoured police car is pelted with rubbish as it moves down a street shortly after the deadline for a city-wide curfew passed on April 28, 2015Shannon Stapleton/Reuters

Rioters plunged part of Baltimore into chaos on Monday, torching a pharmacy, setting police cars ablaze and throwing bricks at officers hours after the funeral of a man who died from a severe spinal injury he suffered in police custody.

Monday's riot was the latest flare-up over the mysterious death of Freddie Gray, whose fatal encounter with officers came amid the national debate over police use of force, especially when black suspects are involved. Gray was African-American.

Baltimore Freddie Gray
A firefighter uses a saw to open a metal gate while fighting a fire in a convenience store and residence in the early morning hours of April 28, 2015Eric Thayer/Reuters
Baltimore Freddie Gray
Baltimore city firefighters gather near a home which was set ablaze in west Baltimore on April 28, 2015, after the funeral of Freddie GrayAdrees Latif/Reuters
Baltimore Freddie Gray
A protester walks through thick smoke after several buildings were set ablaze by rioters in Baltimore, on April 27, 2015Jim Bourg/Reuters
Baltimore Freddie Gray
Firefighters respond to a blaze at a CVS pharmacy on Pennsylvania Avenue in Baltimore on April 27, 2015Sait Serkan Gurbuz/Reuters
Baltimore Freddie Gray
A burnt-out CVS pharmacy is seen on April 28, 2015, the day after it was looted and set ablazeAdrees Latif/Reuters
Baltimore Freddie Gray
A fire hose cut by rioters sprays water into the air as firefighters attempt to extinguish a burning building during clashes in Baltimore on April 27, 2015Jim Bourg/Reuters
Baltimore Freddie Gray
The remains of a senior centre in Baltimore smoulder at dawn on April 28, 2015, after a night of riotsMark Makela/Getty Images
Baltimore Freddie Gray
Baltimore police officers tackle and arrest suspected looters as they emerge from a Deals store in Baltimore on April 27, 2015Jim Bourg/Reuters
Baltimore Freddie Gray
Mourners grieve by the coffin of Freddie Gray, who died following an arrest by the Baltimore police department, at Woodlawn Cemetery in Baltimore, on April 27, 2015Shannon Stapleton/Reuters
Baltimore Freddie Gray
A demonstrator confronts police near Camden Yards, home of the Orioles baseball teamSait Serkan Gurbuz/Reuters
Baltimore Freddie Gray
A protester wears a Baltimore police department hat that was taken out of a damaged police car on April 25, 2015Shannon Stapleton/Reuters
Baltimore Freddie Gray
Demonstrators confront law enforcement officers near Baltimore Police Department Western District on April 25, 2015Sait Serkan Gurbuz/Reuters

Baltimore is actually two cities. One is the decaying, crime-ridden area that inspired the gritty television police drama "The Wire". The other is a successful, gleaming city on the waterfront attracting increasing numbers of young affluent residents.

In Baltimore, African-Americans make up nearly two-thirds of the city, one of the largest black populations in absolute and relative terms in cities in the United States. In the Sandtown-Winchester area of Baltimore, where people clashed with police on Monday, nearly 90% are black.

Of the area's residents older than 24, about 57% have not advanced beyond a high school education, 15 percentage points above the national average, according to census data. A third of the homes there are vacant.

By contrast, in the Roland Park area on the more affluent north side of the city, the poverty rate is 10.2%. That zipcode is 80% white, and more than 90% of people older than 24 have attended at least some college.

In the 1950s Baltimore was the sixth largest city in the United States with a peak population of nearly 950,000. Now it ranks 26th, with a population of around 620,000. One quarter of the city's residents live in poverty.

Baltimore is one of the less equal American cities when measured by income and educational achievement. It was ranked 12th out of 50 major US cities in the inequality reading. (Atlanta - which was one of the American cities hit hardest by the housing bust - was the most unequal, according to the Brookings study that covered 2007-2013.)

Baltimore Freddie Gray
Protesters clash with police during a march in honour of Freddie Gray in Baltimore on April 25, 2015Alex Wong/Getty Images
Baltimore Freddie Gray
After being Tasered by police, a man is led by officers to an ambulance on April 25, 2015. Four men were arrested after breaking windows and attempting to loot shops following a gathering of hundreds of protestersMark Makela/Getty Images
Baltimore Freddie Gray
A Baltimore police officer takes cover during clashes with protesters in the streets near Mondawmin MallBrendan Smialowski/AFP
Baltimore Freddie Gray
A mixture of milk and water rolls down a man's chest in an attempt to neutralise pepper spray on April 27, 2015Chip Somodevilla/Getty Images
Baltimore Freddie Gray
National Guard troops stand watch along East Pratt Street in Baltimore, on April 28, 2015Eric Thayer/Reuters

The economic divide may have provided some of the tinder that led to looting and arson in the city. Growing income inequality has emerged as a key theme ahead of the 2016 presidential election with both Democrats and Republicans calling for the issue to be addressed. President Barack Obama has termed income inequality and the inability to move up the ladder as "the defining challenge of our time".

In a paper published last year, Raj Chetty of Harvard University and his co-authors found the Baltimore area ranked near the bottom of major US cities in terms of mobility.

According to the study, someone born into the bottom fifth of the population in Baltimore stood 6.4% chance of making it to the top one-fifth of the income strata. That compared with an 11% chance in Washington, DC.