Hard-right euroskeptic George Simion won the first round of Romania's presidential election rerun on Sunday, near final results showed, after a ballot seen as a test of the rise of Donald Trump-style nationalism in the European Union.

Ballots from nearly 99.6% of voting stations showed Bucharest Mayor Nicusor Dan, 55, was in second place at around 21%, behind Simion's 40.6%. They will meet in a runoff on May 18.

A Simion victory could isolate the country, erode private investment and destabilize NATO's eastern flank, where Ukraine is fighting a 3-year-old Russian invasion, political observers say.