An explosion tore through an apartment building in southern Ukraine, killing at least 17 people and leaving dozens more trapped under the rubble, emergency officials said Thursday.

Up to 700 rescuers were searching for survivors in the wreckage of the collapsed five-story building in the Crimea peninsula resort of Yevpatoriya after a blast Wednesday caused by a suspected gas leak, the Emergency Situations Ministry said.

Ministry spokesman Volodymyr Ivanov said at least 17 had been killed, saying a higher initial toll was based on some double-counting of bodies.

The explosion occurred at around 9:45 p.m., when most of the destroyed section's 62 registered inhabitants would have been home, ministry spokesman Ihor Krol said earlier. Two children were among the dead, he said.

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"There was a loud bang, and we rushed out and saw half of the building was missing," witness Sergei Yurchenko told Russian state television Channel One. "There were screams, and a child was crying."

Ukrainian state television pictures showed military rescuers searching for survivors among mounds of concrete and glass. A middle section of the building was missing, and apartments on either side were exposed with walls missing. The rescuers fell silent every hour to listen for possible cries for help.

The blast destroyed 35 apartments, said Krol, adding 21 people had been rescued, with four of them hospitalized.

President Viktor Yushchenko and Prime Minister Yulia Tymoshenko were flying to Yevpatoriya, according to their Web sites.

"This is a terrible, irretrievable loss for all the relatives and those close to those who perished," Yushchenko said in a statement.

Tymoshenko said in televised comments that the survivors would be given housing before year's end.

Russian President Dmitry Medvedev offered to send naval personnel from Russia's Black Sea fleet, stationed at the Ukrainian port city of Sevastopol, to help with the rescue, but Yushchenko said in comments carried by Russian agency ITAR-Tass that help wasn't required.