Flash mobs of slum teenagers in Brazil's upscale shopping malls are spreading, and stirring black activism for greater social justice, experts say.
Since last month, the "rolezinhos," or flash mobs, have occurred mostly in Sao Paulo but they are now catching on in more cities, including Rio de Janeiro and Campinas.
Shopping centers have responded by boosting their private security and securing court injunctions to close their premises -- or to get police to keep protesters out.
At a protest Saturday, angry demonstrators unfurled a banner proclaiming "In the World Cup country, racist malls deny entry to black and poor people."
It is a turn of events authorities do not relish as Brazil readies to host the high-profile sporting event -- they'd no doubt prefer to focus on smiles and sunshine and not overcoming the legacy of slavery.
The flash mobs were started in Sao Paulo by followers of Funk Ostentacao, an urban musical style that extols flashy, brand-name clothes and expensive cars, according to Rafael Alcadipani, a professor at the Getulio Vargas Foundation in Sao Paulo.
"This is a way for underprivileged kids to express their creativity and energy," according to Eduardo Alves, a director of the Rio-based Slum Monitor.
"They are trying to say that the city belongs to all, that they have the right to get together anywhere, including in middle-class and wealthy areas.
"They don't want to be confined in shantytowns."
Ignacio Cano, a social sciences professor at Rio de Janeiro State University, said most of the flash mobs are peaceful.
"What is wrong with these youngsters congregating in malls?" he asked.
"There is a deep, irrational fear that when poor, black kids get together, they are going to do something wrong," he noted.
Cano warned that legal attempts to bar the teens from shopping malls based on their appearance carries "a high risk of discrimination" and could be counterproductive for store owners as it will hurt their business.
Flash mobs spotlight 'structural racism' in Brazil
"These teenagers from the slums have found a new popular model for a successful protest," said rights leader David Santos.
The flash mobs, made public on social media, expose Brazil's "structural racism," said Santos, who heads Educafro, a leading civil rights group championing work and educational rights of blacks and indigenous people.
More than half of Brazil's 200 million people are of African descent, the world's second largest black population after that of Nigeria.
Most Afro-Brazilians are descended from the millions of Africans brought here during colonial-era slavery that ended nationwide only in 1888.
Over a century on, Afro-Brazilians complain of widespread racial discrimination and disproportionate poverty.
Blacks and other slum dwellers generally stayed out of the massive street protests that brought hundreds of Brazilians out on the streets last June to demand a better quality of life and an end to rampant corruption.
Their focus has been on denouncing on what they called a "genocide of black youths" allegedly carried out by police in the country's shantytowns.
But the new restiveness among young people in poor neighborhoods appears to be spurring greater black political activism, particularly on social media.
Saturday, militants representing various black civil rights groups and leftist student organizations staged a protest outside the JK Iguatemi shopping center in Sao Paulo in solidarity with the flash-mob movement.
The posh mall shut its doors saying it was not equipped to handle the demonstrators.
Though the protest drew only 150 people, Douglas Melchior, an activist of the UNEafro black civil rights group, told AFP that it was supported by thousands of people on Facebook.
In Niteroi, near Rio, 50 youths late Saturday stormed the Plaza Shopping center in another flash-mob protest to denounce "racism."
Meanwhile black militants are vowing to keep the pressure on.
The flash-mob activism challenges the "fundamentally racist, segregationist nature" of Brazilian society," said Joselicino Junias, a member of the anti-racism organization Circulo Palmarino.
"We are going to demand public policies to create citizenship mechanisms for these young people -- as well as recreational and cultural activities for them," said Melchior.
Politicians are trying to defuse tension and promote dialogue.
Sao Paulo state governor Geraldo Alckmin said police would intervene only if the flash mobs ended up turning into violence and vandalism.
And local officials are trying to arrange meetings with both sides to work out an acceptable compromise, including offers of public spaces for recreational activities for poor youths.
But more flash-mob protests are planned, including one urging thousands of youths to go to Shopping Leblon, in Rio's posh southern zone, on Sunday.
Any police overreaction ran the risk of hastening "another eruption of mass social unrest," warned Alcadipani.
The World Cup is to kick off in Sao Paulo on June 12.