Minister of Electricity Ahmed Shaker has apologised for power cuts that have been ongoing in various parts of the country since Thursday morning.
He vowed to solve the problem before the end of the day.
"I promise we will do as much as we can and God willing the power outage will never happen again," Shaker said in a statement.
"There are no indications the outage was intentional and I will not come to any conclusion until after a thorough investigation," he added.
Earlier on TV, Shaker said sabotage was not the cause of the outage.
According to a statement by Egypt's electricity holding company, at 6:15am a technical malfunction took place at Cairo's "500-kilowatt" electricity transformer substation, leading to an electricity blackout in various parts of the city.
Shaker said the national electricity grid could produce 20,000 mega-watts before the crisis, but this had been reduced to 11,000 mega-watts.
The outage was not caused by fuel shortages, he added.
He denied the government had used the Aswan High Dam water reservoir to generate additional electricity. The dam produces nearly 12 percent of Egypt's electricity.
Governorates in Upper Egypt also suffered power cuts.
By Thursday afternoon, electricity had started to return in many parts of the country.
The unprecedented blackout caused huge financial losses in Suez city after steel and other factories were forced to shut down.
The outage also paralysed telecommunications in the city, which led the Red Sea port authority and the Suez Canal authority to declare an emergency situation. According to preliminary estimates production losses in Suez reached LE100 million.
Alexandria electricity holding company boss Mohamed Ali Baker said power cuts in the city were the result of nationwide problems.
He said the problem would continue throughout Thursday until the technical malfunction was solved.