The Romanian capital, Bucharest, has seen one of its largest ever anti-government protests after a decree was passed that could free dozens of officials jailed for corruption.
A crowd of at least 150,000 was reported outside government offices late on Wednesday and rallies took place in other towns and cities.
As the protesters dispersed, a group of football supporters threw firecrackers at police who responded with tear gas.
The decree was passed late on Tuesday.
The leftist government, led by Prime Minister Sorin Grindeanu of the Social Democratic Party (PSD), only returned to power in December after protests forced its last leader from power in October 2015.
The new government says the decree is needed to ease overcrowding in prisons but Mr Grindeanu's critics say he is trying to release allies convicted of corruption.
The unfolding crisis prompted a cabinet minister to resign on Thursday.
Business and entrepreneurship minister Florin Jianu appealed on Facebook for stability to be restored and said he was standing down for the sake of his son. "How I am going to look him in the eyes...? Will I tell him that his father was a coward?" he wrote.
The protests came hours after the EU warned Romania against "backtracking" in its efforts to beat corruption.
"The fight against corruption needs to be advanced, not undone," said European Commission head Jean-Claude Juncker.
"We are following the latest developments in Romania with great concern."
What sparked the protests?
The emergency decree decriminalises several offences and makes abuse of power punishable by incarceration only if the sums involved are more than €44,000 (£38,000; $48,000).
One immediate beneficiary would be the PSD leader, Liviu Dragnea, who faces charges of defrauding the state of €24,000.
Others due for release include elected officials and magistrates.
The protests began several days ago, attracting the support of centre-right President Klaus Iohannis. He was part of a judicial watchdog's decision on Wednesday to challenge the decree in the constitutional court.
Mr Dragnea, 54, has become a focal point for the protesters and is already barred from office because of an earlier suspended jail sentence for voter fraud.
The protesters massing in Bucharest on Wednesday night chanted "Resign" and "Thieves, thieves".
"Our chances are small but it is important to fight," said architect Gabriela Constantin.
Another protester, Nicolae Stancu, said: "We came to protect our country against criminals who tried to dismiss the rule of law in Romania; to protect our rights and interests, not their obscure interests."
Demonstrators accused local football hooligans loyal to the ruling party of trying to sabotage their protest by targeting police. Witnesses told the BBC that a group of at least 100 "ultras" threw smoke bombs and stones at police, leaving two police officers and two protesters hurt.
President Iohannis praised the conduct of protesters across the country and criticised the authorities' handling of the groups that, as he put it, tried to "break" the Bucharest demonstration.