BELGRADE, Serbia (AP) — Voters in Serbia are casting ballots in a presidential election seen as a test of public support for populist Prime Minister Aleksandar Vucic and his autocratic rule.

Vucic, an ultranationalist turned a pro-EU politician, is slated to win by a high margin against 10 opposition candidates. His political clout could face a blow, however, if he does not sweep his opponents in the first round of voting Sunday.

Vucic needs to win by more than 50 percent of the vote to avoid a runoff election on April 16 that would put him in a much trickier position against a single opposition candidate.

Vucic, prime minister since 2014, is expected to use his win to appoint a figurehead successor and transform the presidency from a ceremonial office into a more muscular role.