Zimbabwe's state-owned power company said it lost generating capacity at its main plants yesterday, cutting the supply to Harare's CBD.
Distribution had been disrupted "across the country", Fullard Gwasira, a spokesman for Zesa Holdings, said.
The company is trying to restore generating units at the Kariba hydropower and Hwange thermal-power facilities.
"It isn't clear how long it will take to rectify the faults but we are working as fast as we can," the company spokesman said.
Parts of the capital have not had electricity for two days. The country, which has the world's biggest known reserves of platinum and chrome after South Africa, produces an average of 1300MW of power compared with peak demand of 2200MW, resulting in daily rationing and blackouts that have paralysed mines and industry, according to the Confederation of Zimbabwe Industries.
Zimbabwe's Chamber of Mines, whose members include Impala Platinum Holdings' Zimplats unit, and the Mimosa mine that Impala jointly owns with Aquarius Platinum, did not answer phone calls.
Ben Bvumaranda, who owns a luxury furniture-making business, said he had sent his workers home.
"I'll call them back when power is restored, but I have had no electricity since last night and I can't get through to Zesa's fault desk. We have no idea how long this will last," he said. "All we know is it's costing money."