At least 64 people have died in a fire that tore through a shopping and entertainment complex in the Siberian coal-mining city of Kemerovo, BBC reports.
Many of the victims are children, Russian officials say, with 10 people still listed as missing.
The blaze started on an upper floor of the Winter Cherry complex while many of the victims were at the cinema.
Video posted on social media showed people jumping from windows to escape the flames on Sunday.
"According to preliminary information, the roof collapsed in two cinemas," Russia's Investigative Committee said in a statement.
The cause of the fire is not yet known and authorities have launched an investigation.
The region's deputy governor Vladimir Chernov was quoted as saying the fire began in a children's trampoline room.
"The preliminary suspicion is that a child had a cigarette lighter which ignited foam rubber in this trampoline room, and it erupted like gunpowder," he said.
Kemerovo, a key coal-producing area, lies about 3,600km (2,200 miles) east of Moscow.
Russia's commissioner for children's rights, Anna Kuznetsova, blamed negligence, and called for urgent safety checks at similar entertainment complexes.
Some 660 emergency personnel were deployed in the rescue effort. Firefighters tackled the blaze for more than 17 hours.
The shopping centre, which opened in 2013, includes a multiplex cinema, restaurants, a sauna, a bowling alley and a petting zoo. All the animals at the zoo are reported to be dead.
Eleven injured victims are being treated in hospital, suffering from smoke inhalation. The most serious case is an 11-year-old boy whose parents and siblings died in the fire, Health Minister Veronika Skvortsova said.
The fire is believed to have started at around 17:00 (10:00 GMT) on Sunday in a part of the building that contains the entertainment complex, local media report.
Yevgeny Dedyukhin, deputy head of the Kemerovo region emergency department, said the area of the fire was about 1,500 sq m.
"The shopping centre is a very complex construction," he said. "There are a lot of combustible materials."
Four people have been detained for questioning, including the head of the company that manages the shopping centre, according to the Investigative Committee. The owner of the Winter Cherry complex is among those detained.
Russian officials had initially given a figure of 64 people missing but later clarified that this included victims whose remains had not been identified.
At least nine of the bodies found so far are children.
Andrei Mamchenkov, deputy head of Russia's National Crisis Management Centre, said 41 children were not accounted for.
An Instagram post from Kemerovo showed a big queue of volunteers waiting to donate blood at a clinic.
Emergency services finally reached a cinema hall on the third floor after being obstructed by smoke and the danger of collapsing masonry, an unnamed source told Russian news agency Interfax.
They found no bodies inside but fear people may have been buried under rubble.
Another source told the agency there was practically no chance of finding survivors.