Croats were voting on Sunday in a presidential run-off election, with incumbent Zoran Milanovic ahead in opinion surveys of Dragan Primorac of the ruling Croatia's Democratic Union for the chiefly ceremonial position.

Polling stations opened at 0600 GMT and will close at 1800 GMT, with exit polls expected minutes later. Preliminary results will be known around 1900 GMT and official results are expected in the following days.

Around 3.8 million Croats are eligible to vote in the second round. In the first round two weeks ago, Milanovic led with 49.1% support to Primorac's 19.35%.

An opinion poll published on Friday by Nova TV Daily News showed Milanovic of the Social Democratic Party leading with 67.4% against Primorac, a former science minister, with less than 27%.

The Croatian head of state cannot veto laws but has a say in foreign policy, defence and security matters.

During his term, Milanovic, a populist former prime minister, has confronted Prime Minister Andrej Plenkovic over foreign and public policies, with the two men often trading insults.