Romania's prime minister said Thursday his government will push ahead with decrees decriminalising a range of corruption offences, defying the country's biggest protests since the end of communism.

"We took a decision in the government and we are going to press ahead," Prime Minister Sorin Grindeanu said after a meeting in Bucharest of his ruling left-wing Social Democrats (PSD).

PSD chief Liviu Dragnea meanwhile blamed the overnight demonstrations, reportedly involving up to 300,000 people, on an "ongoing campaign of lies and disinformation".

"The PSD won elections (in December) with a huge vote. The government's power is legitimate," he said, accusing President Klaus Iohannis of being the "moral author of last night's violence".

The demonstrations were largely peaceful although a small group of football ultras, according to the authorities, hurled firecrackers and bottles at police, who responded with tear gas.

Dragnea also denied that he would benefit from one of the new government decrees, issued late Tuesday, that makes abuse of power punishable by prison only if the sums involved exceed 44,000 euros ($47,500).

Dragnea, 54, is currently on trial for alleged abuse of power involving 24,000 euros. He is currently also serving a two-year suspended sentence for voter fraud that bars him from office.

"I talked to my lawyers. The decree does not put an end to my trial. The false accusation against me remains in place," he told reporters.