38 parties and 7 coalitions are taking part in the elections.
A party should gain at least 4% of the votes to get into parliament.
The leader of the former ruling party Citizens for European Development of Bulgaria Boyko Borisov expressed readiness to head the country's government again, the Voice of Russia reported.
The opposition Socialist Party has nominated financier Plamen Oresharsky for prime minister.
Borisov's Cabinet resigned following mass protests against high electricity prices in February.
On Thursday, Bulgaria's Parliament dissolved itself after several weeks of protests against high energy bills and poverty turned violent and ousted Boyko Borisov's government.
Earlier this week, Bulgaria's President Rosen Plevneliev said that the early parliamentary elections will be held in the country on May 12th.