The latest opinion polls gave Parvanov, a 49-year-old former Socialist leader who has shepherded his country entry into the European Union next year, a commanding lead over his two closest rivals with some 43-55 percent of the likely votes.
However there were fears that less than 50 percent of the electorate may bother to vote, which would mean a second vote on October 29, with the risk of an ultra-nationalist candidate making the running.
Opinion polls indicated that the turnout could in fact fall below 50 percent of the 6.4 million voters, with some estimates as low as 34 percent.
In the event of a second-round vote, Parvanov would have to confirm his re-election against either the ultra-nationalist firebrand Volen Siderov, 50, or the compromise right-wing candidate Nedelcho Beronov, 78.
And while surveys at the beginning of the campaign saw Siderov neck and neck with the former constitutional court chairman Beronov, support for the sharp-tongued nationalist quickly surged as the vote drew near.
The less charismatic and lesser known Beronov strived to motivate voters by warning them that if he did not make it into the run-off, they would be forced to support Parvanov to eliminate firebrand Siderov.
Such a situation could be similar to that in France in 2002, when the French Socialists were forced to support conservative Jacques Chirac in order to defeat extreme-right nationalist Jean-Marie Le Pen.
In the latest surveys Siderov polled about 20-29 percent of the intended votes against 10-22 percent for Beronov.
Political analysts also warned that Siderov will most probably receive an additional so-called "hidden vote" from people who support him but are reluctant to admit it when asked by pollsters.
Ever since he appeared on the Bulgarian political scene ahead of general elections in June 2005, Siderov has ridden on public disillusionment to scoop up the protest vote and squeeze his Ataka party into parliament.
He opposed Bulgaria's current involvement in Iraq and Afghanistan as well as an agreement to set up three US military bases on Bulgarian soil.
A powerful populist speaker, he lashed out against both the left- and right-wing governments in office since the fall of communism, calling them "robbers" who sold off formerly state-owned factories at bargain prices and agreed to shut facilities at Bulgaria's only nuclear power plant at Kozloduy to join the EU.
"They have pushed Bulgaria to its knees ... and now say: 'Forget who robbed you and dance the Vienna waltz as you will soon be Europeans'," Siderov said in his last rally on Friday.
He called Parvanov "a Turkish puppet" for his good relations with the Turkish minority party in Bulgaria, and also lashed out at Bulgaria's 10-percent Roma minority.
Parvanov, a former leader of the Socialist (ex-communist) party, has become Bulgaria's most popular and trusted politician since he took office in 2001.
Under his leadership, Bulgaria joined the North Atlantic Treaty Organisation in 2004 and this year received the green light to join the European Union on January 1, 2007.
Bulgaria's president is elected for a five-year term in a direct vote but plays a mostly ceremonial role, although he is the official head of state and commander-in-chief of the armed forces. Presidents can serve no more than two successive terms.
Polling stations opened at 6:00 am (0300 GMT) and balloting was scheduled to conclude 13 hours later at 7:00 pm .
The first exit polls were expected to be released shortly after voting ends, while the first partial official results were expected around 9:30 pm.

Copyright AFP (Agence France-Presse), 2006