A law enforcement source told TASS there was a blast at the Sennaya Square metro station. No official confirmation or casualty report was immediately available.
The local rescue services told TASS they were responding to the report of the smoke, but could not provide any detail.
At least three stations of the metro have been reportedly closed for passengers.
Some of the images show several bodies lying next to the damaged car, with blood apparently spilt on a bench.
RIA Novosti said evacuation of people from the affected area was underway.
The metro management said they received reports of an explosion inside the car, possibly of an improvised explosive device.
Photos taken near the Sennaya Ploshchad station entry showed firefighter vehicles involved in responding to the emergency.
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