Bulgarians voted Sunday in the second-round run-off of presidential and local elections, largely tipped by analysts to tighten the ruling right-wing GERB party's grip on power.

GERB's presidential candidate, former construction minister Rosen Plevneliev, holds a commanding lead of 40 percent after the first-round vote last Sunday. He faces Socialist Ivaylo Kalfin, who garnered 29 percent.

The battle will be hard-fought, however, as the Socialists scramble to keep hold of the job, following the two successive five-year terms of incumbent Georgy Parvanov who cannot stand again.

Bulgaria's president is elected in a direct ballot for a five-year term in office but has a largely ceremonial role, apart from being the commander-in-chief of the armed forces.

The top job is however particularly coveted by GERB as it would give the right-wing party full control of power.

GERB already has a near-majority in parliament, while its minority cabinet is also safely buttressed by a handful of independent lawmakers.

Although Plevneliev holds a commanding lead after last week's first-round vote, the outcome was far from certain as Meglena Kuneva, the former European commissioner who had come in third in the first-round vote with 14 percent, had not endorsed either of the candidates.

Riding on the huge personal popularity of Prime Minister Boyko Borisov, the party is also expected to win most mayoral seats in the parallel local run-offs Sunday.

It already took the capital Sofia and three other big cities in the first round, and is sending 18 more of its big-city mayoral candidates to run-offs.

GERB had also won the most city council seats in 20 of the 27 regional centres last Sunday.

Massive election fraud and vote-buying allegations had however marred its victory.

The more complicated two-in-one elections together with new voting rules caused administrative chaos in polling stations last Sunday.

Many of the 6.9 million eligible voters could not cast a ballot because of voting list discrepancies and huge lines outside stations.

A record number of between six and 10 percent of the ballots was also declared invalid, raising eyebrows by anti-corruption watchdog Transparency International and prompting numerous objections.

The release of official results by the central electoral commission was also delayed well after the 48-hour deadline.

Polling stations opened at 6:00 am and were to close at 7:00 pm (1700 GMT), with the first exit poll results expected to be released shortly after polls close.