"Today is a very important day. I have personally voted for a modern, European, normal Romania and call on all Romanians to take part in the election", the president said, as cited by the news agency Agerpres.
The president added that the future of the country depended on Sunday's vote.
According to Romania's Central Election Commission, as of 10:00 a.m. (08:00 GMT), 6.87 percent of registered voters have cast their ballots in the runoff.
The second-round of Romania's presidential election is taking place on Sunday, after neither Iohannis nor his political opponent, former Prime Minister Viorica Dancila, secured a majority to win on 11 November. Iohannis won 37.82 percent and Dancila won 22.26 percent.