A Moscow Metro subway train derailed during the morning rush hour, killing at least 20 people and injuring more than 150, reports The Independent. So far, the rescue operation has lasted for over seven hours, as the train derailed underground between two stations. Russian officials are reporting that they have evacuated 1,100 passengers from the derailed train.

Officials initially said a power surge had triggered an alarm that caused the train to stop abruptly and come off the tracks, mangling the cars inside the tunnel. However, reporters were later told that a power surge was not the cause. Investigators are looking into if there was a fault in the train cars or a dip in the ground, says The Independent.

Officials didn't believe the accident was an act of terror, despite the frequency in which Moscow's airports and public transportation systems have been hit with terrorist attacks over the last two decades.

Segei Sobyanin, the mayor of Moscow, said officials would be fired if they were found to have any part in the disaster, and could face criminal charges if the investigation finds negligence or wrongdoing, says The Independent.

The derailment happened on the Arbatsko-Pokrovskaya line, the longest in Moscow at 28 miles, between Slavyansky Bulvar and Park Pobedy stations. Park Pobedy is the deepest metro station the system, at 275 feet underground, which is making the rescue particularly hard.

Read more from The Independent HERE.