Russia has launched dozens of missiles at cities across Ukraine, officials there say.
Kyiv Mayor Vitaly Klischko said there had been several blasts in the city, causing damage and at least one death.
The attacks happened two days after Russia carried out one of the largest air strikes since the start of the war.
Ukraine President Volodymyr Zelensky had warned Russia could launch more attacks to make Ukrainians “celebrate the New Year in darkness”.
Mykolaiv Governor Vitaly Kim said on Facebook that Russian missile launches had been reported.
“The occupiers have decided to try to spoil the day for us,” he said.
In Kyiv, amid New Year celebrations, people rushed to shelters as air raid sirens sounded at lunchtime.
Emergency workers were sent to three districts hit by explosions. Air defence has been activated in regions across the country.