Romanian police used tear gas and pepper spray to quell anti-corruption protesters in Bucharest Friday, as tens of thousands called on the leftwing government to resign.

Local media said between 30,000 to 50,000 people turned out for the protest, including many Romanian expatriates who returned home to show their anger at the levels of official corruption.

The crowd chanted "resign" and "thieves" as they assembled in a central square outside the main government building.

Hundreds of protesters tried to break through the police cordon and officers in riot gear responded with tear gas and pepper spray, forcing the demonstrators back.

Nearly 250 people required medical attention after inhaling tear gas and pepper spray, while 10 police officers were injured by hurled stones and bottles, the emergency services said.

Stefan and Ileana Anghel, Romanian nationals living in Spain, waved a Spanish flag after travelling across Europe to take part in the demonstration.

"Unfortunately nothing has changed in Romania," Ileana told AFP.

"We want to see modern roads and schools and above all to not have to pay bribes to the left and right," added Ileana who, like her husband, works in the Alicante region.

Last month Romanian President Klaus Iohannis sacked top anti-graft prosecutor Laura Codruta Kovesi, who was considered a symbol of the fight against graft in one of the EU’s most corruption-plagued members.

EU's richer members are paying price for Eastern states' endemic corruption

With Kovesi at the helm, the Anti-Corruption Prosecutor’s Office (DNA) had led a crackdown on corruption among local and national elected officials in recent years, earning accusations of abuse of power and the enmity of many in Romania’s political class.

Among the protesters in Bucharest on Friday was 60-year-old Vlad and his wife who flew in from New York where they have lived for 30 years.

"Corruption and embezzlement, which profit the ruling class, are what bothers me," said Vlad, an estate agent in the US.

"A force is being born here (at the protest) and I hope that the message is heard," he added.

Thousands of people also joined demonstrations in other main Romanian cities, including Cluj in the northwest, central Sibiu and Timisoara in the west.

Around four million Romanians work abroad from an overall population of 20 million. Half of the expatriates are living in Italy and Spain, according to official figures.

Last year those working abroad sent 4.3 billion euros back to their families at home, nearly 2.5 percent of the national GDP in one of Europe’s poorest countries.