According to officials, a wave of Russian missiles has hit cities across Ukraine.
According to Kyiv Mayor Vitaly Klitschko, several bombs exploded in the capital, killing at least one person. A hotel has also suffered damage.
The attacks came just two days after Russia launched one of the largest air strikes since the war began.
Ukraine President Volodymyr Zelensky had warned Russia could launch more attacks to make Ukrainians “celebrate the New Year in darkness”.
In recent months, Russia has targeted Ukraine’s energy sector, destroying power plants and plunging millions into darkness during the country’s bitter winter.
Several senior Ukrainian officials have mentioned the strikes in social media posts, saying that Russia will not be able to ruin their celebrations.
“The occupiers have decided to try to ruin our day,” Mykolaiv Governor Vitaly Kim wrote on Facebook.
Valerii Zaluzhny, the head of Ukraine’s armed forces, said air defenses had shot down 12 of 20 Russian cruise missiles.
People in Kyiv rushed to shelters as air raid sirens wailed.
According to Ukraine’s spy chief, the battlefield is deadlocked.
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Emergency personnel were dispatched to several districts affected by explosions.
Mr Klitschko said that 20 people were injured in Kyiv, including a Japanese journalist.
On Telegram, Deputy Presidential Chief of Staff Kyrylo Tymoshenko stated that a hotel had been damaged.
Across the country, air defense has been activated.
A drone attack in the western city of Khmelnytskyi injured two people, Mr Tymoshenko added.