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

City Hall officials gave the death toll as 10. At least 106 people were hospitalized, of whom 50 are in grave condition, Itar-TASS said, quoting Moscow's health department chief, Georgy Golukhov.

An Associated Press journalist saw injured people taken out of the station on stretchers. At least 15 ambulances were standing by, while four helicopters took off from the lawn nearby.

Golukhov told Russian television that only one person is still trapped in a wrecked train car but he is alive. However, emergency services at the scene speculated that there could be more.

Yuri Akimov, a Moscow representative of the emergency services, said in a televised briefing outside the Park Pobedy station that about 200 people were evacuated from the train, which was stuck between two stations in west Moscow.

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

Park Pobedy is the deepest metro station in Moscow, 84 meters (275 feet) deep, which is making the rescue particularly hard.

While accidents are regular occurrences in the Moscow Metro, deadly incidents are rare.