State media reported that more than 100 people were hospitalized, 50 of whom were in critical condition.
The incident took place during the morning rush hour in the Russian capital. Three metro train cars derailed in a tunnel, ITAR-Tass reported.
More than 200 people have been evacuated, the Emergency Ministry said on its website.
Dozens of ambulances arrived at the scene, along with three BK 117 helicopters, to help shuttle the injured to hospitals, according to ITAR-Tass.
It was not clear what caused the derailment, but the head of Moscow’s Transportation Department said it was not a terrorist attack.