A metro train derailed in Moscow, Russia on Tuesday, leaving 10 people dead.

Of the 106 people hospitalized, 50 are in critical condition.

The incident took place during the morning rush hour. Three metro train cars derailed while in an underground tunnel, the state-run Itar-Tass news agency reported.

More than 200 people have been evacuated, the emergency ministry said on its website.

It was not clear what caused the derailment, but the head of Moscow’s transportation department said it was not a terrorist attack.