Exit polls in Bulgaria show ruling party candidate Rosen Plevneliev the likely winner of Sunday's presidential election, but without enough votes to avoid a runoff.

The polls give Plevneliev about 40 percent of the vote, while his closest challenger, Socialist candidate Ivailo Kalfin, has about 30 percent. If officials uphold the results, the two will meet again next Sunday for round two.

European election monitors report cases of vote-buying and voter intimidation. But Bulgarian officials say that overall, the election was problem-free.

Bulgaria's economy has been the key campaign issue, with opposition candidates accusing the ruling conservative GERB party of stalling key reforms.

The country is experiencing only modest economic growth, with unemployment remaining a problem. But Bulgaria is not expected to seek an economic bailout like several much larger and richer European Union economies.

The winner of the election will replace President Georgi Parvanov, who is barred by the constitution from seeking a third five-year term.