With a scant 28 days left before the World Cup, the streets of Brazil have been filled with burning barricades, armored military vehicles, and thousands of indignant citizens demanding that their voices be heard.

In São Paulo, an estimated 1,200 protesters gathered Thursday evening on Paulista Avenue as part of the International Day of World Cup Resistance — a series of demonstrations coordinated across the country to express public discontent ahead of the mega athletic event.

(Photo by Guilherme Prado)

As the procession began, a giant skeleton wearing a Brazilian jersey danced among the crowd while protesters performed theatrical skits, played music, and erected banners.

(Photo by Eva Hershaw)

At the end of the street, a projector beamed government-spending statistics (“Only 0.4 percent of the resources going to the World Cup is private investment”) onto the façade of a large building. The march, organized by the Popular Committee for the World Cup, appeared to be one of the most creative, orderly expressions of resistance yet.

“R$2 billion” — more than $900 million — “spent on repressive operations.” (Photo by Guilherme Prado)

“We have rights and we want them to be guaranteed,” Juliana Machado, a member of the Popular Committee for the World Cup, told VICE News as the protesters prepared to march. “We’re here not only to defend these rights, but to reclaim the rights that we’ve lost in the run-up to the World Cup.”

But less than a half an hour into the demonstration, events quickly shifted. A confusing and uneasy stir moved through the crowd. Protesters along Consolação Avenue started yelling insults at police officers, who walked together behind shields alongside storefronts on the periphery of the procession.

Before anyone could really understand what was going on, a loud explosion rang out. The police had fired a stun grenade. This was followed by screams, more explosions, and the rapid descent of a police helicopter, which blew up dust and beamed a spotlight onto demonstrators as they quickly dispersed into side streets.

Footage from Thursday's protest in São Paulo shows the march devolving into chaos as police launch stun grenades.

Video footage illustrates the moment of tension, but it remains unclear what action on the part of protesters, if any, had prompted the police to detonate stun grenades.

Reports offer diverging accounts of what transpired shortly before the upheaval. Some accuse protestors of provoking the police, throwing rocks and other pieces of trash towards the huddled group of officers. Others insist that the grenades were an unjustified and disproportionate response to little more than heated verbal exchanges between protesters and the police.

(Photo by Eva Hershaw)

As protesters scattered and businesses pulled down metal screens over their storefronts, black bloc members took advantage of the chaos and began smashing bank windows. They also vandalized a Hyundai dealership — the car manufacturer is an official World Cup sponsor — before setting trash aflame in the street.

(Photo by Guilherme Prado)

In the end, eight people were detained by the military police and at least four people, two of them journalists, were reported injured.

A photojournalist affected by stun grenade thrown by police is helped by people protesting the World Cup in Sao Paulo — Agence France-Presse (@AFP)May 15, 2014

The day included several protests by teachers, metalworkers, and metro employees elsewhere in São Paulo. The city’s transport department later said that demonstrations had resulted in traffic jams stretching more than 90 miles.

“We have to use the World Cup to apply more pressure,” Vitor Ribeiro, a leader of the metro workers’ union, remarked to VICE News ahead of Thursday’s rallies. “The metro is going to be the only way for tourists to get to the Itaquerão stadium, and a strike would do a lot of damage. They know this, and so do we.”

Earlier in the day, an estimated 5,000 members of the Homeless Workers’ Movement (MTST) protested the government’s failure to address their housing demands by marching to the Itaquerão stadium, where they set fire to car tires. For the past two weeks, more than 4,000 families have occupied an encampment called the People’s Cup in an empty tract of land near the stadium.

(Photo via Juntos)

“The clock is ticking: they have 28 days to resolve not only the People’s Cup but all the occupations that are part of this fight,” MTST leader Guilherme Boulos said in a press statement. “If this isn’t resolved, there will be problems.”

In Recife, in the northern state of Pernambuco, protests prompted the government to deploy the military to control looting in the absence of the local police force, which is on strike. It marked the second time that the Brazilian government has sent soldiers to patrol a World Cup host city in the last two months.

Military vehicles are shown patrolling the streets of Recife.

As burning trash was cleared from São Paulo’s streets, organizers of the International Day of World Cup Resistance were already busy planning their next move. News of a mass demonstration planned for May 31 quickly began circulating on social media.

When Machado, the protest organizer, was asked what message she and her compatriots were trying to convey, she answered, “We’re going to see fighting in this World Cup. It’s simple — that’s it.”