Updated 14.24

At least 20 people are now known to have died in a metro train derailment in Moscow. 150 others were injured in the accident, which is being blamed on a power surge.

Officials have ruled out any terrorist involvement.

Several carriages left the track in a tunnel after a power surge triggered an alarm and appeared to make the train slam on its brakes.

At least 106 people were also taken to hospital, of whom 50 are in a serious condition, Itar-TASS said, quoting Moscow's health department chief, Georgy Golukhov.

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

Helicopters landed in the street to take the most seriously injured to hospital and around 60 ambulances were also at the scene.

One survivor told the Rossiya 24 channel that he "thought it was the end". "There were lots of injured" he added. "Various injuries: heads, legs".

The accident happened at the Park Pobedy station

Another witness told Life News television "I got into the carriage and after about 20 seconds, the light went out and the train was just pulled apart...Panic started".

Park Pobedy is the deepest metro station in Moscow, 275-feet deep, making the rescue particularly hard.

Photos on social media showed passengers walking along the tracks inside the dimly lit tunnel. They also appeared to show carriages piled on top of each other.

A city transport spokesman said all passengers had been evacuated, dismissing earlier reports that people were still trapped. While accidents are regular occurrences in the Moscow Metro, deadly incidents are rare.

Opened in 1935, the ornate subway system carries some nine million people everyday.

Suicide bombings killed 40 people in 2010 but there is no suggestion of foul play causing today's incident.