"We are angry as a provincial government, and what has happened was equal to an act of terrorism," Mazibuko told reporters on Friday.
She said the matter was being investigated by various agencies, including the Hawks, and that the people behind the power disruptions had endangered people's lives.
City Power's managing director Sicelo Xulu said it had realised that switches at a number of substations had been tampered with.
"There was no forced entry, and that simply means that someone turned them off," said Xulu.
He said that City Power had put in place security measures at substations around the city to ensure the disruptions did not happen again.
Xulu said some of the areas still affected included Lenasia, Alexandra, Randburg and some areas in the Johannesburg city centre.
'Laying criminal charges'
"The process of laying criminal charges has been undertaken," said Johannesburg mayor Parks Tau.
He said the labour relations process had to be respected, but that a situation where residents were deprived of electricity could not be allowed.
Earlier in the day City Power management updated him on the restoration of electricity in some parts of Gauteng.
Power was disrupted in parts of the West Rand and northern Johannesburg after a few hundred City Power staff downed tools on Wednesday afternoon. City Power said the strike was not union-led.
The workers were unhappy about a new shift system being implemented
It was believed that striking workers had sabotaged infrastructure, causing widespread blackouts, which affected traffic flow and some businesses' operations.
Despite claims by residents about power not being restored to areas such as Houghton, City Power said that electricity had been fully restored by noon to areas including Houghton and Melville on Friday. City Power also said it was expected that other parts of Johannesburg could remain in the dark over the weekend.
The electricity supply had also been reconnected in Auckland Park, Kew and Bramley. – Sapa