Sao Paulo, Brazil (CNN) -- With barely a month until the World Cup opens in Brazil, violent protests and strikes are breaking out across the country by groups angry about the changes the sporting event has brought -- and what it hasn't.
Demonstrations were held in 18 cities Thursday. The biggest and most violent was in Sao Paulo, where police shot tear gas and protesters threw rocks and smashed the windows of a car dealership and a bank.
While thousands of people took part in the protests, they were still much smaller than the massive marches seen during the Confederations Cup last year when tens of thousands took to the streets.
In the morning, the Homeless Workers Movement blocked main avenues across the city and about 4,000 people marched on the Arena Sao Paulo where the inaugural game of the World Cup will be held on June 12.
Demonstrators accuse the government of spending billions on new stadiums and not enough on low-income housing.
"The World Cup has done nothing to help us," said Diana, a manicurist who has been on a list for a government-subsidized house for a decade. "So we decided to use it as a platform to make our voices heard."
Taking advantage of the global attention focused on the country for the world soccer championship, other groups are staging protests to air their grievances.
Across the country in Recife, also a World Cup venue, soldiers were deployed to rein in crime and looting after police went on strike there.
In Sao Paulo, more than 5,000 striking teachers marched to demand higher wages.
In the evening, a string of anti-World Cup protests were staged in different cities.
In Sao Paulo, activists turned out carrying banners that said "FIFA go home" and "A World Cup without the people means we're back on the street again!"
About 1,500 people marched peacefully for a couple of blocks before clashes erupted.
Anti-World Cup protesters and homeless activists vowed to keep up the pressure through the global event that ends on July 13.
A total of 600,000 foreign visitors are expected for the cup and another three million Brazilian fans are expected to travel around the country.