MOSCOW — The theater was packed, and children’s movies were on the screens when the smoke began billowing in. When panicked audience members rushed for the exits, they found them blocked.

Many used their phones to plead for help, among them Viktoria Pochankina, an 11-year-old girl on a class trip to the Siberian mall where a fire on Sunday killed at least 64 people, many of them children.

“She called me at 4:11 p.m. the last time and told me that everything was in flames, and that the doors were blocked in the cinema, and that she cannot get out,” Viktoria’s aunt, Yevgeniya Oganesyan, told the newspaper Komsomolskaya Pravda.

“I told her: Vika, take off your clothes and take them to your nose, breathe through your clothes,” Ms. Oganesyan said. “She told me, ‘Tell Mummy that I loved her.’”