Earlier, officials have asked Ukrainians who sought refuge abroad not to return during winter months to conserve energy, as infrastructure remains a target of Russian attacks.
Ukrainian authorities have begun evacuating civilians from recently liberated sections of the Kherson and Mykolaiv regions, fearing that a lack of heat, power and water due to Russian shelling will make living conditions too difficult this winter.
They urged residents of the two southern regions, which Russian forces have been shelling for months, to move to safer areas in the central and western parts of the country.
Ukrainian Deputy Prime Minister Iryna Vereshchuk said Monday that the government would provide transportation, accommodations and medical care for them, with priority for women with children, the sick and the elderly.
Vereshchuk last month asked citizens now living abroad not to return to Ukraine for the winter to conserve power.
Other officials have suggested that residents in Kyiv or elsewhere who have the resources to leave Ukraine for a few months should do so to save power for hospitals and other key facilities.
Ruthless winter weather worries WHO
The WHO delivered a chilling warning Monday about the energy crisis' human impact on Ukraine.
"This winter will be life-threatening for millions of people in Ukraine," said the WHO's regional director for Europe, Dr Hans Henri P. Kluge.
"Attacks on health and energy infrastructure mean hundreds of hospitals and healthcare facilities are no longer fully operational, lacking fuel, water and electricity."
He warned of health risks such as respiratory and cardiovascular problems from people trying to warm themselves by burning charcoal or wood and using diesel generators and electric heaters.
The evacuations are taking place more than a week after Ukraine recaptured the city of Kherson, on the western bank of the Dnieper River, and surrounding areas in a major battlefield gain.
Since then, heading into the winter, residents and authorities alike are realizing how much power and other infrastructure the Russians damaged or destroyed before retreating.
Ukraine is known for its brutal winter weather, and snow has already covered the capital Kyiv and other parts of the country.
'More than half' of Ukraine's energy facilities damaged in Russian strikes
Russian forces are fortifying their defence lines along the Dnipro river's eastern bank, fearing that Ukrainian forces will push deeper into the region.
In the weeks before Ukraine's successful counteroffensive, Russian-installed authorities relocated tens of thousands of Kherson city residents to Russian-held areas.
On Monday, Russian-installed authorities urged other residents to evacuate an area on the river's eastern bank that Moscow now controls, citing intense fighting in Kherson's Kakhovskiy district.
Russia has been pounding Ukraine's power grid and other infrastructure from the air for weeks, causing widespread blackouts and leaving millions of Ukrainians without electricity, heat and water.
To cope, four-hour or longer power outages were scheduled Monday in 15 of Ukraine's 27 regions, according to Volodymyr Kudrytsky, head of Ukraine's state grid operator Ukrenergo.
Ukrenergo plans more outages Tuesday. Ukrainian President Volodymyr Zelenskyy says Russian missile strikes have damaged more than 50% of the country's energy facilities.
Zelenskyy on Monday repeated his calls for NATO nations and other allies to recognize Russia as a terrorist state, saying its shelling of energy facilities was tantamount "to the use of a weapon of mass destruction."
Zelenskyy also again urged stricter sanctions against Russia and appealed for more air defence aid.
"The terrorist state needs to see that they do not stand a chance," he told NATO's 68th Parliamentary Assembly meeting in Madrid in a video address, after which he said the body approved the terrorist designation.