19 residents have been pulled out alive from the shattered block in the Black Sea resort of Yevpatoria in the Crimea peninsula, said Emergencies Ministry spokesman Ihor Krol, adding that at least 24 people were missing.
Emergencies Minister Volodymyr Shandra earlier told Ukraine's Channel 5 television that between 40 and 80 people could be under the rubble.
The cause of the blast on Wednesday night had not been established yet but it was "quite possible that there had been containers with oxygen or acetylene stored in the building", Krol said.
Prime Minister Yulia Tymoshenko flew to Yevpatoria, a government photographer accompanying her told Reuters. President Viktor Yushchenko was due to travel to the disaster-stricken town shortly, his press service said.
Officials said the blast sent concrete cascading down on two entrances to the building.
"As I was walking by, I heard a bang, and then I saw this building crumble," an eye-witness told Ukraine's Channel 5 television.
Some 700 Emergencies Ministry workers were excavating the rubble, looking for survivors. From time to time, they paused in silence, and incoming mobile phone calls were heard from under huge piles of the debris, Channel 5 said.
Cranes were being used in the rescue efforts. A total of some 90 machines were working at the scene.
Casualties caused by gas blasts in often crumbling apartment buildings are common occurrences in former Soviet republics, particularly in winter when residents use more heating.
One such blast in October 2007 killed 15 residents in Ukraine's central city of Dnipropetrovsk.
Last Mod: 25 Aralık 2008, 14:38