Hundreds of rescuers are working in the rubble of an apartment building in southern Ukraine, where an explosion has killed at least 22 people, BBC reported.
Emergencies Minister Volodymyr Shandra said 21 people have been rescued. Many more people are feared to be trapped.
Two entrances to the five-storey building in Yevpatoria were blocked by falling concrete following the blast.
The cause is unknown, although officials say that gas cylinders may be to blame.
Rescuers have been scrabbling through the rubble, calling for quiet to hear cries for help.
One resident, Lidia Kovalenko, told AFP news agency: "I saw a blue flame and smoke and... a horrible explosion."
There were about 35 flats in the building, which was built in the 1960s.
Ukraine President Viktor Yushchenko has declared 26 December a national day of mourning.
The president and his political rival, Prime Minister Yulia Tymoshenko, travelled in the same car to the site of the blast in Ukraine's Crimea peninsula.
Ms Tymoshenko said initial reports suggested dangerous materials were stored without permit in the basement.
Russian President Dmitry Medvedev expressed his condolences and said his Black Sea fleet was ready to help.
Yevpatoria is a popular summertime resort.
Correspondents say casualties caused by gas explosions in often crumbling apartment buildings are common occurrences in former Soviet states, particularly in the winter, when residents use more heating.
One such blast in October 2007 killed 23 residents in the central Ukrainian city of Dnipropetrovsk.