Police fired tear gas and rubber bullets Tuesday as an attempt to evict homeless families from an unused former hotel in Sao Paulo turned violent.
Residents hurled furniture and projectiles from windows into the street below as police sallied to evict them.
The clashes spread into nearby streets as groups of protesters set up barricades and torched a bus near the municipal theater in the heart of the city of some 20 million.
Local media reports quoted a homeless pressure group as saying some 200 families, around 800 people, had occupied the former hotel six months ago.
Sao Paulo is Brazil's richest city but also one with the most acute housing shortage.
The city hall estimates the shortfall at some 700,000 housing units, and many homeless people have simply occupied abandoned buildings.
Broadcaster Globo reported one policeman as injured in the confrontation but military police could not confirm the claim.