Police said fans of a football team caused much of the violence Sunday, the fourth day of protests.
About a hundred youths threw rocks rocks, firecrackers and smoke bombs, the Tanjug news agency reported.
Demonstrators vandalized stores, burned cars and set garbage bins on fire, police said.
Police said they fired tear gas, pushing troublemakers away from the city's central square.
The Sunday violence grew out of what began as a peaceful demonstration by 1,000 people calling for President Traian Basescu's resignation over austerity measures and lowered living standards, the Mediafax news agency reported.
A police statement Monday described participants in the violence as fans of a local football team who had been involved in earlier incidents.
The protests began Thursday in support of a Health Ministry official who resigned after criticizing proposed reforms.