Four people have been killed and 15 injured after a bus ploughed into an underpass in Moscow.

Multiple videos show the vehicle swerving off one of the Russian capital's busiest roads at speed at around 3pm local time (12pm GMT).

It collapses down a wide set of steps leading to a subway before being stopped by the tunnel's roof, as panicked passers-by scatter.

Image: The bus left the road and ploughed down the underpass

Passengers on-board and people walking on the steps near the Slavyansky Boulevard metro station were killed.

Moscow police are looking into two possible causes - the driver losing control and a technical problem with the vehicle.


"The driver of the bus began movement and then changed his trajectory, which resulted in the bus going down into the pedestrian underpass," they said.

Image: Passengers and passers-by were injured in the crash

"The driver has been detained. Police employees are working with him."

They did not mention terrorism as a possible cause.

They also revised the number of dead confirmed in an earlier statement from five down to four.

Image: The bus stopped when it crashed into the subway roof

The Russian Investigative Committee, which probes major crimes, added: "According to the driver, the bus was parked and suddenly began to move by itself.

"Despite his attempts to stop the bus, the breaking system did not work and the bus continued moving."

Image: Five people were killed in the crash

Traffic spokesperson Artyom Kolesnikov confirmed: "A bus drove into a pedestrian underpass."

Moscow mayor Sergei Sobyanin tweeted: "There are dead and wounded. We are providing emergency aid."

25 December is an ordinary working day in Russia, as Orthodox Christmas is not celebrated until 7 January.