(Reuters) - Romanian riot police used tear gas against protesters who threw rocks and set fire to newspaper stands and rubbish bins in central Bucharest in a fourth day of street demonstrations against government austerity measures Sunday.

Protesters also gathered peacefully in several large cities across Romania, including Cluj, Timisoara and Iasi, calling for the resignation of President Traian Basescu and the centrist government of Prime Minister Emil Boc.

The protests began across the country Thursday in support of a deputy health minister who resigned after criticizing a controversial draft health care reform bill that would have added private firms to the state health sector.

The Cabinet withdrew the bill Friday, but that did little to assuage the demonstrators, who returned to the streets to express general discontent with spending cuts and falling living standards.

The Bucharest protests Sunday were the most violent seen since the start of the financial crisis. Although the government cut state jobs and wages and raised value added tax in 2010, Romania has largely avoided the kind of violent anti-austerity protests seen elsewhere in Europe.

Demonstrators threw rocks at riot police who in turn fired tear gas into the crowd.

Several shop windows were broken. Rubbish bins and newspaper stands were torched between the University of Bucharest and Unirii square in the city center.

More than 50 people required medical assistance and about 40 demonstrators were detained by police for inciting vandalism, police and emergency medical unit officials were quoted as saying by the Mediafax news agency.

Protesters had started gathering in the afternoon, with numbers growing to an estimated 1,000 in the evening.

Carrying whistles and Romanian flags, the protesters chanted Resignation and held banners that said We want respect and No more corruption.

The government has taken painful but needed measures under a two-year aid deal led by the International Monetary Fund to shore up state finances and stabilize the leu currency. But the measures have been deeply unpopular as Romania's economy recovers from a two-year recession.

The start of the protests Thursday was triggered by the resignation of Deputy Health Minister Raed Arafat, who had criticized the draft health care reform bill.

Arafat was only the spark, said Jean Sandulescu, 63, a railway worker. But after everything they have done, we want them (the government) to go.

Riot police estimated up to 4,000 Romanians staged protests Saturday in more than 20 cities, although the actual numbers may be higher. Demonstrations were largely peaceful, but in Bucharest some protesters threw stones at riot police who fired tear gas into the crowd Saturday evening.

Traffic on one of Bucharest's busiest streets was temporarily blocked and a few dozen people, including three riot police, needed medical attention.

It is unlikely the government will cave in to protests, although they pile more pressure on the ruling Democrat Liberal Party, which is clearly losing even more support, said political commentator Mircea Marian.

Let's see what next week will bring, although I don't think protests can continue for much longer. People have jobs.

(Reporting by Luiza Ilie and Bogdan Cristel; Editing by Peter Graff)

Health Care Reform IMF International Monetary Fund International Monetary Fund