MOSCOW — A rush-hour subway train derailed Tuesday in Moscow, killing at least 20 people and sending more than 100 others to the hospital, many with serious injuries, Russian emergency officials said.

Several cars went off the track in the tunnel after a power surge triggered an alarm, which caused the train to stop abruptly.

Russian Emergency Situations Ministry Vladimir Puchkov gave the casualty toll at a televised news conference. At least 50 of the injured are in grave condition, the Itar-TASS news agency said, quoting Moscow health department chief Georgy Golukhov.

PHOTO: Driver of crashed Moscow Metro train among others trapped inside carriage http://t.co/HIux4K9XzZ pic.twitter.com/jHEXpuFkII — RT (@RT_com) July 15, 2014

Golukhov told Russian television that only one person is still trapped in a wrecked train car but said he is still alive. Emergency services at the scene, however, speculated there could be more trapped commuters. It was not possible to immediately reconcile the reports.

Terrible accident in the #Moscow #Metro. My most sincere condolences. I wish the victims health and strength in this tragedy — Dmitry Medvedev (@MedvedevRussiaE) July 15, 2014

The Russian capital's airports and transit systems have been hit by several terrorist attacks over the past two decades but officials said Tuesday this appeared to be an accident. Puchkov said terrorism is not being considered as a possible cause.

Photos and videos from social media show injured people being taken out of the Park Pobedy station in west Moscow on stretchers and put into ambulances, while medical helicopters cycled to and from the lawn nearby.

Helicopters on standby at Park Pobedy station to airlift victims of #Moscow Metro accident pic.twitter.com/GCgHMHn27w — Gabrielle T-F (@gabrielletf) July 15, 2014

Yuri Akimov, a Moscow spokesman for the emergency services, said outside the station that about 200 people were evacuated from the train, which was stuck between two stations.

accident in the Moscow subway, affected 30 people. may have died pic.twitter.com/xtmQHXnV72 — Lazov (@LazovG) July 15, 2014

Park Pobedy is the deepest metro station in Moscow's subway system — 84 meters (275 feet) deep, which made the rescue particularly hard. The station serves the vast Park Pobedy, where the World War II museum is located and which is close to Moscow's triumphal arch.

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.

Photos on social media showed passengers walking along the tracks inside the dimly lit tunnel.

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," he said. "It's a miracle we got out. I thought it was the end."

"I was tossed up in the air. There was blood on the floor, heads bruised, arms broken. Panic broke out," one witness, named Ivan, tells RT.

“There was a man next to me and his head had been smashed by the handrail and he was unconscious. Some people had broken ribs and one person’s arm was injured. All in all, people were hysterical," said another.

While accidents are regular occurrences in the Moscow Metro — as this map, written in Russian, shows — deadly incidents are rare. Up to nine million passengers use it every day.