After decisively winning the most votes in Romania's first-round presidential election redo, hard-right nationalist George Simion will face a pro-Western reformist in a pivotal runoff in two weeks that could reshape the European Union and NATO member country's geopolitical direction.

Romanian Prime Minister Marcel Ciolacu resigned on Monday, a day after a far-right opposition leader won the first round of the presidential election re-run and his own candidate crashed out of the race.

Romanian Prime Minister Marcel Ciolacu has resigned and his Social Democrat party is to leave the government after a right-wing nationalist candidate won the first round of the presidential election.