Electricity was cut to Zambia and Zimbabwe at roughly the same time late Sunday, authorities said, with the cause of the nationwide disruptions under investigation as power was being restored.
Power supply went down Sunday evening in both countries, which have for months only been receiving around seven hours of electricity a day as drought empties their main provider of hydropower, the Kariba Dam.
"Government wishes to inform the nation that last night at 20:15 hours, a power outage occurred, affecting the entire country," the Zambian government said in a statement.
No deaths or critical incidents were reported at Zambia's main hospital, the University Teaching Hospital, as back-up systems operated as expected, it said.
Power was restored to the hospital after 30 minutes, it added, without saying when the rest of the country returned to normal supply.
"Technical teams are currently investigating the cause of the outage and working to prevent similar incidents in the future," it said.
The Zimbabwe Power Company (ZPC) said Monday that its national grid "experienced a system disturbance last night, resulting in a system blackout."
The power cut started in Zimbabwe at around 8:25 pm, reports said. By morning, most load centres were again operational, ZPC said.
The countries are already only getting about seven hours of national power a day with water levels dropping at the gigantic Kariba Dam, the largest source of hydroelectricity for both countries that sits on their border.
The water level available for power generation was 2.40 percent on November 18, according to the Zambezi River Authority which manages the dam.
The dwindling national power supplies in both countries has led many to turn to alternate options, notably solar energy.