Citizens of Ukraine have been advised to leave the country – if they can – to help reduce demand on the energy network.
Ukrainians should consider leaving for “three to four months” as it “will be very helpful to the system,” Maxim Timchenko, the head of Ukraine’s biggest private energy supplier has said.
Almost half of the country’s energy system has been damaged by attacks launched by Russia since it started its invasion in February.
Kyiv has called on Ukrainians to limit their use of home appliances such as ovens and washing machines in a bid to conserve energy.
Mr Timchenko, chief executive of DTEK, told the BBC that the energy system becomes less reliable each time Russian troops launch missiles at the power infrastructure.
Such attacks have increased since Russia suffered setbacks in battle, such as Ukraine’s recapture of Kherson, in the south of the country, last week.
Since then, Russia has carried out more than 148 missile strikes on critical infrastructure, leaving approximately 10 million people without power, Ukrainian officials said.
Ukrainians have been left without power during both scheduled and unscheduled blackouts, while temperatures are dropping – with some regions experiencing below-zero temperatures.
Mr Timchenko suggested that people reducing their energy use would help Ukraine win the war.
He said: “If you consume less, then hospitals with injured soldiers will have guaranteed power supply. This is how it can be explained that, by consuming less or leaving, they also contribute to other people.”
Fixing the damaged infrastructure is also becoming more difficult as Ukraine has run out of equipment and spare parts. Mr Timchenko called on “partners, government officials, companies and equipment producers to help with the immediate supply of available equipment”.
Meanwhile, Rishi Sunak has visited Ukraine to meet Volodymyr Zelensky and announced a £50m new package of air defence support.
The visit is Mr Sunak’s first since he became the UK’s prime minister less than a month ago. His predecessor Boris Johnson had visited twice and developed a friendship with the Ukrainian president.
Mr Sunak said: “We are today providing new air defence, including anti-aircraft guns, radar and anti-drone equipment, and stepping up humanitarian support for the cold, hard winter ahead.
“It is deeply humbling to be in Kyiv today and to have the opportunity to meet those who are doing so much, and paying so high a price.”
During the visit, Mr Sunak also confirmed £12m for the World Food Programme’s response to Ukraine, and £4m for the International Organisation for Migration.
Downing Street said the funding would help provide generators, shelter, water repairs and mobile health clinics, with the UK also sending tens of thousands of extreme-cold winter kits for Ukrainian troops.
It follows the announcement of more than 1,000 new anti-air missiles, promised to Ukraine by defence secretary Ben Wallace earlier this month. The UK is also planning to send army medics and engineers.
Mr Sunak’s visit comes after a missile hit a Polish village close to the Ukrainian border and killed two men in their 60s. It had sparked concerns that either Russia or Ukraine had struck a Nato member state, potentially escalating the war.
But, on Friday, Ukraine’s air force spokesman Yuriy Ignat reportedly said that so many missiles were fired by Russia and Ukraine that the missile fragments which struck Poland could have been of either Russian or Ukrainian origin.