Infuriated protesters clashed with police as they tried to attack an office of the Water and Power Ministry in Malakand district, northwestern Khyber Pakhtunkhwa province.
Police fired at protesters killing at least two and injuring six others, local news channel Dunya TV reported.
Footage aired on Dunya TV showed thousands of stick-wielding protesters ransacking and burning a police station in Malakand.
Deputy Commissioner Malakand Zafar Ali Shah told reporters that hundreds of enraged protesters burned and rampaged through government offices and police checkpoints.
Mobs led by local parliamentarians also besieged power stations for hours in Charsaddah, Mardan and Peshawar districts of Khyber Pakhtunkhwa.
Protests, many of them violent, were also held in the country's commercial capital Karachi, Lahore and several other districts, where citizens had to bear breakdowns ranging from eight to 14 hours.
The protests erupted as temperatures in the country soared, with several southwestern districts recording a high of 50C (138F).
The Muslim-majority country is also observing the month of Ramadan, when fasting requires abstaining from food and water for up to 16 hours.
Following the violence, Prime Minister Nawaz Sharif called an urgent meeting of the Water and Power Ministry to find ways to reduce long power outages, particularly during Ramadan, state-run Pakistan Television reported.
Sharif, whose Pakistan Muslim League came into power with a landslide victory in 2013, is facing a harsh criticism from his opponents for not containing the long-standing energy crisis in line with his election manifesto.
