Amid widespread dissatisfaction over poverty and corruption, Bulgarians are going to the polls for early parliamentary elections.
The May 12 vote was moved forward from July after center-right Prime Minister Boiko Borisov resigned in February following nationwide protests over high energy prices and economic stagnation.
Opinion polls have suggested a close race between the former ruling party and the Socialists.
The campaign has been roiled by a scandal over illegal wiretapping allegedly ordered by the former interior minister.
On the eve of the elections, prosecutors said officials had seized on Friday 350,000 illegal ballot papers from a printing house.
Opposition activists accused the former government of involvement and raised concerns about electoral fraud.
More than 250 international observers are expected to monitor the vote in the European Union and NATO member state.