Demonstrators in Sao Paulo burned tyres and blocked roads, and police responded with tear gas
Riot police in Brazil have fired tear gas and stun grenades to disperse thousands of people in the city of Sao Paulo who were protesting against the cost of hosting the football World Cup.
Some demonstrators hurled stones while other burned tyres and blocked roads.
They say they are angry that billions of dollars are being spent on next month's football tournament, rather than social projects and housing.
Protests are taking place in many other cities, including Rio de Janeiro.
Aerial images showed hundreds of people marching in rush-hour traffic on a main thoroughfare in the Brazilian city, which will host the final match of the World Cup on 13 July.
Police, teachers and civil servants, among others, have also been on strike across Brazil.
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Most people here will eventually support the World Cup when it gets under way, but it's cost a lot of money - $15bn (£10bn) - and most of that has been public money.
Brazil is still a developing country with many inequalities and high levels of poverty. And when you see brand-new stadiums popping up in a Sao Paulo suburb at the cost of millions, and around there are squatter camps full of people saying they cannot afford to live, then you can see where the conflict comes from.
What the government will be looking out for is a critical mass. If these protests are attracting 5,000-10,000 people every time, then they will become too difficult to police.
The BBC's Gary Duffy in Sao Paulo says that the scale of the protests will be watched closely by the government as an indication of the security challenges they may face during the tournament, which kicks off on 12 June.
He adds that, with both the World Cup and a presidential election this year, many groups have spotted an opportunity to exert maximum pressure on the government.
The demonstrations began earlier in the day in Sao Paulo, with one of the biggest protests in the city's Itaquera district near the Arena Corinthians stadium, which will host the tournament's opening match.
Protesters there demanded housing, and not stadiums, be built in accordance with Fifa standards, in reference to world football's governing body.
'No panic'
"Our goal is symbolic," said Guilherme Boulos, the head of Homeless Workers Movement.
"We don't want to destroy or damage the stadium. What we want is more rights for workers to have access to housing and to show the effects the Cup has brought to the poor."
One protest in Sao Paulo was held near the stadium which will host the tournament's opening match
The government has tried to downplay the scale of Thursday's unrest, arguing it was not related to the World Cup.
"From what I've seen, these are specific claims by workers. I've seen nothing that is related to the (World) Cup," Brazilian Sports Minister Aldo Rebelo said.
"There's no reason to panic ahead of receiving three million Brazilian tourists and 600,000 foreign tourists (for the tournament)."
Army deployed
The planned protests coincide with a range of strikes, including one by the police force in the north-eastern state of Pernambuco.
The army has been deployed there to provide additional support after some robberies and looting, as the strike enters its third day.
Recife, the state capital, is due to host five matches during the World Cup.
Recent protests in Brazil have been much smaller than those which took place in June last year in various cities.
More than a million people took to the street then over poor public services, corruption and the high cost of hosting the World Cup.
The wave of protests prompted Brazilian President Dilma Rousseff to propose a referendum on political reform.
She also pledged to invest 50 billion reais ($25bn, £16bn) in public transport, one of the protesters' main grievances.
