In the first round of the election two weeks ago, the EU-sceptic Milanović secured 49.1% of the vote, missing out by less than one percent on a thumping first round victory. 

Primorac, a former science minister backed by governing party and Croatia’s prime minister, came in second with 19.4% of support, and looks unlikely come out of the run-off ahead of his rival. 

An opinion poll published on Friday by Nova TV Daily News showed Milanović of the opposition’s Social Democratic Party leading with 67.4% against Primorac, with less than 27%.  

Preliminary results will be known around an hour after polls close, at 1900 GMT, and official results are expected in the following days. 

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

During his term, Milanović has confronted Prime Minister Andrej Plenkovic over foreign and public policies, with the two men often trading insults. 

Before becoming president, Milanović was Croatia’s prime minister from 2011 to 2016.