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.