Officers fired teargas and rubber bullets to disperse crowds who rallied for a second day in Siliana, a city in Tunisia's economically deprived interior on the edge of the Sahara desert, witnesses told Reuters.
The hospital in the town of Siliana said 22 injuries had to be evacuated to the capital for treatment, reported the Associated Press.
Residents have been demonstrating for more jobs and government investment in this economically deprived interior region. They are also calling for the resignation of the local governor and the release of 14 imprisoned activists.
Police said they were only defending themselves when demonstrators attacked the government building. But Nejib Sebti, head of the labor union that organized the protests, said they were peaceful until residents were attacked by police.
A medic from Siliana Hospital who did not wish to be named said more than 200 people had been injured in the clashes.
A journalist from France 24 television told Reuters he and a colleague had been hospitalized for wounds from birdshot apparently fired by riot police.
State television said that at least 80 people were injured and that residents blocked the entrances to the city, setting tyres alight on roads.
Iyed Dahmani, a politician from the Republican Party in the town, said the national guard - an interior ministry-run security force - had deployed tanks to help restore order.
The protests were the fiercest since hardline Salafi Islamists attacked the U.S. embassy in Tunis in September over an anti-Islam film made in California. That violence left four people dead.
Prime Minister Hamadi Jebali has accused both Salafis and liberal elites of harming Tunisia's economy and image through their conflict with each other. His Ennahda party has tried to present itself as a middle way between liberals and Salafis.
The World Bank on Tuesday approved a $500 million loan to Tunisia to help it recover from the uprising, with another $700 million loan coming from other donors.
The loan, the World Bank's second since the revolution, aims to support Tunisia's economic recovery by providing funds to improve the business and financial sectors and reform social services.