Homes and businesses have suffered rolling blackouts, known as load-shedding, for up to eight hours in the last couple of days, paralysing industry and mining in the southern African country and damaging an already fragile economy.
"There will be an increase in load-shedding until the situation returns to normal," state utility ZESA said in a statement.
Hwange thermal power station in the northwest of the country, which produces 500-600 MW of power, had halted production due to a "fault that caused a malfunction," it added.
Lack of fresh investment has left the former British colony relying on ageing plants and a worn out grid, resulting in frequent faults and blackouts.
Harare has licenced independent producers to complement ZESA's output, but most of the projects are yet to take off because of concerns over investment laws that are compelling foreigners to transfer majority stakes to local blacks.
Zimbabwe produces 1,200 MW of electricity, most of it from Hwange and a hydropower station on the Kariba dam. It also imports 600 MW from Zambia, Mozambique and the Democratic Republic of the Congo to meet current demand.