Thousands of protesters have gathered in front of the CEZ headquarters in Sofia.
The rally, which started at the Orlov Most junction, then moved in front of the Parliament building, then returned to Orlov Most, has stopped in front of the headquarters of the power distributor.
There is increased police presence.
The protesters are booing and shouting "Down with CEZ" amid calls of the police to disperse.
Bulgaria has seen mass protests in a number of cities over high electricity prices.
In a bid to appease public discontent, Prime Minister Borisov vowed that a procedure for withdrawing the license of CEZ would be started, which was subsequently rejected.
Meanwhile, Prime Minister Boyko Borisov announced Wednesday morning that the center-right GERB government would resign collectively by noon.
The step follows a series of mass protest rallies against high electricity prices that morphed into wider discontent over austerity and the way the country is being run.
Borissov told MPs on Wednesday that his party would not be part of a caretaker government.
Bulgaria's Parliament is to vote on the Cabinet's resignation on Thursday.