The power deficit in Ukraine was running at 30% as off 11 a.m. local time (4 a.m. ET), according to the country's state-run electricity company.
The deficit on Monday was 27%, Ukrenergo said.
The deficit has been caused by the emergency shutdown of "several power plants" on Monday morning, as well as the increase in consumption given weather conditions, the company said in a statement.
It urged Ukrainians to be "economical" with consumption to "allow less application of restrictions aimed at preventing accidents" and also to enable urgent repairs to take place.
A recent barrage of Russian strikes devastated energy supplies in Ukraine, leaving millions of people across the country without access to heat and power amid plummeting temperatures this winter.
Ukrainian first lady Olena Zelenska appealed to the British public not to forget the "tragedy" facing her country this Christmas, days after it marked nine months since the first day of Russia’s invasion.
"I realize that nine months is a very long time, and Ukrainians are very tired of this war, but we have no choice in the matter. We are fighting for our lives. The British public do have a choice: They can get used to our tragedy and concentrate on their own important things in life," she said in a BBC radio interview on Tuesday.
But she added: "It’s not just a war for our freedom and our lives. This is the war of opposing worldviews: A war of values. It’s important that these are preserved."
The first lady’s words come amid relentless Russian attacks on Ukraine’s critical infrastructure, which have left millions of civilians without power and bracing themselves for a freezing winter with no central heating.
Zelenska said Russia was aiming "to terrorize people in Ukraine this coming winter, to scare us that we might not survive the cold, the darkness, without internet."
"The winter is treacherous, and that’s what Russia leaders are counting on.
"Luckily, we are resilient. It would probably be wrong to say that these things do not scare us, they do, but we understand why we can and we should endure this, and we will fight for the world, for electricity and for the light," Zelenska said.
Asked how often she is able to see her husband, Ukrainian President Volodymyr Zelensky, the first lady said: "I can't complain, I'm just like everybody else. I can see my husband a couple of times a week at work because I visit the president's office often, but he rarely sees our children unfortunately."
Zelenska is due to address the British Parliament on Tuesday afternoon.