Five people were killed when a city bus ploughed into a pedestrian underpass in western Moscow on Monday, traffic police said.

It was not immediately clear what caused the accident as authorities said they were looking into several possibilities, including a technical malfunction.

"A bus drove into a pedestrian underpass," a traffic police spokesman, Artyom Kolesnikov, told AFP.

"According to preliminary information, five people died."

Footage broadcast on national television showed a bus driving onto the pavement and then down the stairs of the underpass, running over several pedestrians before coming to a stop.