Around 440 people, including 24 police officers, were injured during an overnight mass demonstration against government corruption in Bucharest, emergency services announced on Saturday.
The protesters were demanding the resignation of the government, objecting to the perceived efforts to weaken the judiciary by the governing Social Democrats (PSD).
Hundreds wound up injured when the police responded with tear gas and water cannons.
Romania's President Klaus Iohannis, a critic of the government, said he "firmly condemned the brutal intervention of riot police", which he called disproportionate reaction to a protest where most were peaceful.
"We want to return to Romania, but there's too much corruption and the health care is dismal", she told The Associated Press.
Tens of thousands of people staged peaceful protests in other Romanian cities. They demanded that the Parliament be dissolved, that early elections be held, that a government of technocrats be created, within a unicameral Parliament, which would include 300 senators, 100 of which should be representatives of the diaspora.
The protests were organized and promoted by groups of Romanians working overseas, angry at what they say is entrenched corruption, low wages and attempts by the PSD to weaken the judiciary in one of the European Union's most corrupt states. Protesters threw bottles at police and other items. Reuters reported that at least 400 people sought medical attention and that the protests were organized in large part by Romanian expats working outside of the country.
Past year those working overseas sent 4.3 billion euros ($4.9 billion) back to their families at home, almost 2.5 percent of the national GDP in one of Europe's poorest countries.
A small group had attempted to storm government offices and clashed with riot police. The AP said that Georgian Enache, a police spokesman, said the police pushback on Friday was "legitimate state violence" because protesters were refusing to leave despite warnings.
In a controversial move last month, Romania sacked top anti-graft prosecutor Laura Codruta Kovesi - considered a symbol of the country's fight against corruption.
Prime Minister Viorica Dancila, in turn, accused Iohannis of "inciting the population against the authorities" and "using the dramatic effects of the events".
Around 150,000 protesters gathered in Bucharest after the Social Democrats took power a year ago following the government passing a decree to decriminalise several corruption offences.