Croatian parties scrambled to form a ruling coalition Thursday, a day after an election in which the ruling conservative party won the most seats but not a parliamentary majority.

Prime Minister Andrej Plenkovic's Croatian Democratic Union (HDZ) won 61 seats in the 151-member assembly, near-complete results showed.

A centre-left coalition led by the Social Democrats (SDP) won 42. It was followed by the nationalist right-wing Homeland Movement party with 14 seats.

An ultra-conservative party and a green-left one won 11 and 10 seats each.

The Mozemo (We Can in Croatian) green-left party called parties "from the left to the right who have said over fours years that their main goal is to destroy the corrupt" government to join forces and "oust the HDZ from power".

"That goal is still achievable," it said on Facebook.

Corruption has long been the Achilles' heel of the HDZ, in power in Croatia for most of the time since its independence from Yugoslavia.

Plenkovic meanwhile said Thursday the HDZ was trying to cobble a parliamentary majority while SDP leader Pedja Grbin said the same thing.

The elections were held after a bitter campaign between Plenkovic and left-wing populist President Zoran Milanovic, who campaigned despite a court warning.

The showdown came as the European Union nation wrestles with corruption, a labour shortage, the highest inflation rate in the eurozone and undocumented migration.

For months, Plenkovic and his HDZ seemed poised for an easy victory that would secure his third term as premier.

Plenkovic has stressed on his role in guiding the country of 3.8 million people into the eurozone and Europe's passport-free Schengen area last year.

But in mid-March, Milanovic -- who tops political popularity surveys -- made the shock announcement that he would challenge Plenkovic and become candidate for the Social Democrats.

Milanovic canvassed across Croatia challenging the country's top court ruling that he could only stand in the election if he stepped down as president first.

His mandate expires in January, but he said he would step down if the SDP and its allies secure a majority to form a new government.