Romanian emergency services officials said five people -- three protesters and two law enforcement officers -- were hospitalized with undisclosed injuries.
Video from the Romanian capital showed several helmeted police officers, separated from demonstrators by a barricade, aiming pepper spray at the protesters.
A few people threw flares and other objects at the security forces and pushed dumpsters full of trash into the street. A small fire began later.
Many protesters waved Romanian flags or brought signs.
As Wednesday became Thursday, most protesters had left the square near the building that houses Romania's Cabinet.
Protesters also took to the streets in 50 other cities across the country, including Timisoara, Cluj-Napoca, Iasi, Sibiu, Brasov, Arad, Galati, Craiova, Constanta and Alba-Iulia.
A new decree passed by the Romanian government decriminalizes corruption that causes damage worth less than about $48,000 (200,000 lei).
The measure takes effect in a little over a week. Once it does it will stop all ongoing investigations for this kind of offense and will also prevent the launching of any subsequent probes related to these offenses.
Another decree adopted Tuesday night could also free some officials who are in prison for corruption.
Liviu Dragnea -- president of the Social Democrat Party, which recently took power -- is under investigation over abuse of power allegations and had also previously received a two-year suspended sentence for an elections offense.
Dragnea and other high-ranking politicians stand to benefit from the new law, which was passed by Prime Minister Sorin Grindeanu and didn't need the vote of the Parliament.
European Commission President Jean-Claude Juncker expressed concern over the new law.
"The fight against corruption needs to be advanced, not undone. We are following the latest developments in Romania with great concern."
The embassies of Belgium, Canada, France, Germany, the Netherlands and the United States issued a joint statement echoing Juncker's sentiments.
"We, Romania's international partners and allies, express our profound concern at the actions of the Romanian government on the night of January 31, 2017, which have undermined Romania's progress on rule of law and the fight against corruption over the past 10 years."
The statement continued: "This act, in contravention to the collective wisdom of the entire judicial and rule of law community, credible elements of civil society, and the demonstrated concerns of Romanian citizens over the past two weeks, can only undermine Romania's standing in the international community and risks damaging partnerships that are based on common values, inherent in the guiding principles of the EU and NATO."
The embassies added they hoped the law would be reversed.
"We hope the government of Romania will reverse this unhelpful course. While amendments to existing laws and procedures are occasionally necessary, these changes should be made only in the process of comprehensive and credible consultation with all stakeholders."
Protesters have vowed to take to the streets again Thursday.