The election comes as the former Yugoslav republic faces economic struggles and at a time of strained ties between neighbours in the volatile Balkans, notably with former enemy Serbia.
At 0300 IST, four-and-a-half hours after polling stations opened, turnout was nearly 19 per cent, the electoral commission said. It was some three percentage points less than at the same time in the November elections.
Some 3.8 million Croatians are eligible to cast ballots after a November election produced no absolute winner.
The coalition's five-month rule was marked by a shift to the right amid a growing climate of intolerance, including attacks on independent media and minorities, notably ethnic Serbs.
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Authorities have appeared to turn a blind eye to the far-right surge, but it has sparked global concern and brought already frosty ties with Serbia to their lowest level since Croatia's 1990s independence war.
Polls and analysts have given a slight lead to a coalition led by the main conservative Social Democrats (SDP) of former prime minister Zoran Milanovic, who was in power for four years until November.
The likeliest outcome is a similar scenario to that of the previous vote -- prolonged talks on forming a government and potentially another election.
HDZ is banking on staying in power with a new and more moderate leader, Andrej Plenkovic, who has pledged to move it away from populism and extremism.
"I'm changing the HDZ... My mission is to position it in the centre-right," said the 46-year-old former member of the European Parliament.
HDZ's former junior government partner -- the "Most" party (meaning "Bridge" in Croatian) -- is likely to play kingmaker once again.
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