The Ukrainian authorities have warned people in the capital Kyiv to expect longer power cuts, lasting more than four hours, because of Russian attacks on energy infrastructure.
Rolling blackouts are hitting not only Kyiv but also central regions of Ukraine, including the city of Dnipro.
President Volodymyr Zelensky said about four million people were affected but “shelling will not break us”.
This month Russia launched dozens of missiles and Iranian-made drones.
Ukraine’s energy infrastructure is being pounded by the air attacks – Mr Zelensky says about a third of the country’s electric power stations have been destroyed.