This post was updated at 2 p.m. ET.
At least two subway cars jumped off their tracks in a tunnel in Moscow's metro system during morning rush hour today, injuring more than 160 people, some of them severely, and killing at least 21 others, emergency officials say.
The derailment was reportedly due to an electrical problem. Reports of the number of dead and wounded often fluctuate in situations like this; we'll be updating this post as necessary.
"A total of 139 people out of more than 160 injured... are in the Russian capital's hospitals, 42 of them are in intensive care," reports Russia's Itar-TASS agency, citing a Moscow health official (figures last updated at 2 p.m. ET).
Doctors are treating passengers for wounds that include internal injuries, along with concussions and head trauma, the agency says.
More than 1,000 passengers reportedly left the scene of the crash by walking down the tunnel to nearby stations. There have also been unconfirmed reports that some commuters had been trapped in one of the cars. Images on social media show the crumpled train cars.
"One of the train drivers has not been found yet," Itar-TASS agency reported this morning, adding that an official says the train had been moving at 70 kph (43 mph).
The derailment took place around 8:30 a.m. local time on the Moscow Metro, one of the busiest subway systems in the world. It carries around 7 million passengers a day.
The train was between the Slaviansky Boulevard and Park Pobedy stations on the blue Arbatsko-Pokrovskaya line when "a power outage led to the launch of a false warning that resulted in the sharp stop of a train," reports RIA Novosti, citing Moscow emergency officials.
"Park Pobedy is the deepest metro station in Moscow's subway system — 84 meters (275 feet) deep," The Associated Press reports, "which made the rescue particularly hard. The station serves the vast park where the World War II museum is located."