It was once known as the "Murder Capital of the World," a city beset by a crack epidemic, no-go areas and resulting crime which triggered decades of white flight to the suburbs.

Decades on from its darkest days, however, Washington DC is experiencing an economic boom that has reversed its long-declining population and is shaking up the city's ethnic mix in ways no-one predicted in the 1980s and 1990s.

But long-term residents of the US capital, the first city in the country to have an African-American majority, are increasingly speaking of a downside.

"Washington used to be the Chocolate City, but now it's the Vanilla Swirl, and most of a Vanilla Swirl is white," said Michael, a black man who grew up on H Street, one of several neighborhoods undergoing a dramatic racial upheaval.

The number of African-Americans slipped below 50 percent last year, proving that the words of Michael, a 54-year-old handyman who was willing to give only his first name, are more than anecdotal.

"After five o'clock it's all Caucasians," he said, pointing to the many bars, restaurants and smart cafes where mostly white, college-educated workers descend to mingle and party after work.

"It's all about the dollar," he said, standing with friends outside the St John Ford Memorial Church of God where he works and volunteers.

"Bars are replacing libraries, and the only people in them are white," he said. "There's no blacks here in the evenings," he added, saying that a strong police presence is on hand to put the area's new patrons at ease.

More than a decade of "gentrification" initiatives have helped Washington rebound and the capital mostly rode out the housing crash with prices now back on the rise.

Homes near H Street -- downtown in one of the capital's earliest commercial districts -- valued at only $100,000 five years ago are now typically selling for around $500,000.

And while H Street retains numerous, fast food eateries and several hair and beauty salons predominantly used by black women, menus are starting to change to accommodate the "Capitol Hill set" that is moving in.

With cuisine ranging from French to Mexican to Lebanese, one swanky new H Street establishment offers dishes such as Sous Vide Fennel and Artichoke Salad, followed by Chickpea Ravioli in curried coconut sauce with cauliflower.

The prices charged match the bigger wallets of workers drawn to the capital by the magnet of jobs in government, lobbying, law firms and commerce.

H Street, a long avenue that heads into the heart of the city, has been cast as the next Georgetown, an affluent neighborhood filled with world-renowned shops and home to many of Washington's richest people.

Such comparisons may be premature but traditionally African-American areas in Washington such as Columbia Heights, Adams Morgan, and U Street, have fallen like dominoes in recent decades, with whites and Hispanics moving in.

Ricardo Vergara, a Colombian who came to the United States in 1984, and who opened up a Mexican-themed restaurant and bar on H Street three years ago, thinks the trend will only speed up.

With business booming he and his partners will soon add a roof deck and street patio to their "H Street Country Club," a venue whose eclectic offering includes live music and an indoor golf course.

"I would say the majority are white," he said of his customers.

"The street changes at night. It is market forces, but I can see it leaving some longer term residents feeling a little threatened."

While the area was under-served for decades and the entertainment market is still in its infancy, Vergara says four other Mexican restaurants are due to open nearby in the next four to six months.

Other non-entertainment business owners such as Lisa North, who for 13 years has operated the Platinum hair and beauty salon, however are finding trade harder to come by.

"Don't get me wrong, I like the new changes -- the bars, the restaurants. I don't want the neighborhood to go back to the way it looked 10 years ago," said North.

But she estimated her taxes and business rates have jumped around 50 percent in the past year and with local authorities deciding to install rails that will in a few years bring streetcars to the area there is less car parking space.

"That means less business," said North, 45. "I don't want the new bars and the like to push our businesses out."

Tom Sugrue, a professor whose first book, "The Origins of the Urban Crisis," examined the role that race and housing played in the downfall of Detroit, said Washington's boom was coming at a cost.

"If you'd have said 20 years ago that the city's white population was going to rise you would have been laughed out of the room," said Sugrue, who teaches history and sociology at the University of Pennsylvania.

"Washington has become a magnet for folks with money, particularly whites and young professionals," he says, noting that the housing boom benefited property owners but marginalized poorer citizens, mostly blacks, who rent.

"It really has pushed the frontiers of gentrification to places that up to 10 years ago had been considered no-go areas. What that is going to do is push people who are searching for more affordable housing out of DC."

Official figures show that the white flight that followed the Washington riots, triggered by the assassination of civil rights leader Martin Luther King in 1968, is now being reversed, with whites moving back and buying up homes.

About 38 percent of blacks were homeowners in Washington in 2009, compared with 56 percent of whites, according to data from the Brookings Institution.

"The long-term trend is whites moving back into the city. It would be hard not to think that something really dramatic is going on," noted Peter Tatian, a housing policy expert at the Urban Institute think tank in Washington.