Their rival, the centre-right Liberals (PNL) received around 21 percent of the votes, while allies and newcomers to Romanian politics, the anti-corruption party Save Romania Union (USR) was on nine percent.

The PSD's likely coalition partner, the liberal Alde party, won around 6.5 percent, meaning they could secure a majority in the parliament.

The low turnout at the ballot boxes, 39.5 percent, likely aided the PSD's strong showing.

"Romania is an island of stability. I want this stable democracy to remain in place," PSD's leader, Liviu Dragnea, 54, was quoted by AFP.

"This means that all politicians and institutions have to respect today's vote. We should all understand that Romania needs a competent, stable and responsible government," he added.

Dragnea said his party would try to form a coalition with the Alde.

But it's yet to be seen whether he could become prime minister, as he received a two-year suspended prison sentence for voter fraud in April.

This bars him under Romanian law from becoming prime minister, and it would also stop former PM Victor Ponta from returning to power.

The 44-year-old Ponta is on trial for alleged tax evasion and money laundering. He denies the charges.

Corruption clean-up

PSD's revival comes only a year after a deadly nightclub fire in October 2015 at a Bucharest club, which became a symbol for a wider discontent and marked a turning point in calling for an end to corruption.

The fire, in which 64 people died, was blamed on corrupt officials turning a blind eye to a lack of fire precautions and standards.

The corruption crackdown that ensued after the tragic fire forced Ponta to resign.

Since then the country has been run by former EU commissioner Dacian Ciolos, 47, an independent who was backed by PNL and USR.

In the meantime, the National Anti-Corruption Directorate, the agency responsible for the anti-corruption drive, put former ministers, media moguls, and judges under investigation.

PSD's return to power could slow down the drive against corruption. It campaigned with an increase in pensions and other social spending, and tax cuts, in one of the poorest EU countries.