Police and housing activists in Brazil's biggest city clashed violently on Tuesday after authorities evicted about 200 families who had illegally occupied an empty hotel in downtown Sao Paulo.

Protesters hurled rocks and pieces of wood at some of the 250 police troops who showed up to evict an estimated 200 families that had occupied the building's 20 floors for six months.

The confrontation spread to nearby streets and in front of Sao Paulo's Municipal Theater, where some protesters torched a bus. Police fired rubber bullets, tear gas and stun grenades in an effort to disperse the crowd.

After several hours of calm, isolated clashes ignited again as night fell in central Sao Paulo, with protesters blocking some roads in the region.

Earlier, live television images showed some young men wearing gas masks and vandalizing nearby businesses, while others used homemade wooden shields to ward off rubber bullets.

Lt. Col. Mauro Lopes of the Sao Paulo police department told reporters seven people suspected of breaking into a store and of setting the bus on fire had been arrested. Another 60 people were taken into custody for questioning.

Four police officers were injured in the confrontation and taken to nearby hospitals.

Police and members of the so-called "roofless" movement have clashed often in recent months. The movement organizes poor families to move into abandoned buildings, often in central Sao Paulo.

Movement organizers have called on officials to provide more low-income housing in Sao Paulo and other Brazilian cities.