Polls show incumbent center-right President Klaus Iohannis ahead with around 40%, followed by the center-left candidate Viorica Dancila, until last month Romania's prime minister, at 15-22%.
Dancila's Social Democrat government was forced to step down after losing a no-confidence vote in parliament amid corruption scandals and allegations it wanted close control of the judiciary.
Iohannis is a former leader of the National Liberal Party, which on Monday formed a minority government led by Prime Minister Ludovic Orban.
If no candidate wins more than 50% on Sunday, there will be a second round of voting on Nov. 24.
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