At least 19 people were killed Tuesday when a Moscow subway train derailed during the morning rush hour, sending at least 150 others to the hospital.
Emergency officials told The Associated Press that at least 50 of those injured were in grave condition.
Alexander Gavrilov, deputy chief of the Moscow emergency services, said rescuers have recovered 7 bodies and are working to extract 12 more bodies from two wrecked train cars.
Several cars left the track after a power surge triggered an emergency alarm, which caused the train to come to an abrupt stop in a tunnel between two stations in the western part of the Russian capital.
Moscow's transit system has been previously targeted by terrorists but this time Russian officials have vehemently dismissed terrorism as a possible cause.
Vladimir Markin, spokesman for the Investigative Committee, said in a televised briefing that investigators were considering a fault in the train cars among the possible causes.
Yuri Akimov, a Moscow representative of the emergency services, said in a briefing outside the Park Pobedy station that about 200 people were evacuated from the train.
Injured people were being taken out of the subway station on stretchers and photos on social media showed passengers walking along the tracks inside the dimly lit tunnel.
Paramedics carried one woman covered with a blanket to the lawn by the famous Triumphal Arch and put her on a medical helicopter, one of four seen taking off from the park.
In the scorching summer weather authorities provided drinking water to survivors, some of whom were sitting near the station's entrance in a state of a shock.
Golukhov told Russian television that one person is still trapped in a wrecked train car but he is alive. Emergency services at the scene, however, speculated there could be more trapped commuters. It was not possible to immediately reconcile the reports.
A man with a bloody cut on his brow told Rossiya 24 television outside the Park Pobedy station that he felt a jolt and the train abruptly came to a halt. "There was smoke and we were trapped inside," the man said. "It's a miracle we got out. I thought it was the end.
At 275 feet below street level, Park Pobedy is the deepest metro station in Moscow, which is making the rescue particularly hard.
The Moscow Metro is one of the most famous subway systems in the world, known for its palatial interiors with mosaics, chandeliers and marble benches. The station serves the vast Park Pobedy, where the World War II museum is located and which is close to Moscow's triumphal arch.
While accidents are regular occurrences in the Moscow Metro, deadly incidents are rare.