A bus left a road in Moscow before ploughing into a subway entrance, leaving at least five people dead and 15 injured, Russian media say.
CCTV video shows people scattering as the vehicle ran down the subway's wide steps before being brought to a halt by the tunnel's roof.
The incident occurred near Slaviansky Boulevard station in western Moscow.
The cause of the incident was not immediately clear but there was no suggestion it was a terror attack.
Ria-Novosti and Interfax news agencies said the driver told police the vehicle started to move suddenly. He tried to apply the brakes but they did not work, the agencies said.
Interfax reported that the bus was not even a year old.
A preliminary examination showed the driver of the bus was sober, it added. He has been held by police.
In July 2014, 21 people were killed when a train derailed near the same station after braking abruptly.
Monday is a normal working day in Moscow, where the Orthodox Christmas will be celebrated on 7 January.
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