A train driver on the Moscow metro died after apparently falling out of a moving train, Russian investigators said Sunday.

The incident took place late Saturday as the train was travelling along a busy line in southern Moscow, the Investigative Committee said in a statement.

"A train pulled into Ryazansky Prospekt metro station without a driver, using automatic braking," investigators said.

"Two minutes later, the driver of the next train found the driver's body under the live rail in the tunnel between Kuzminki and Ryazansky Prospekt stations." 

It was unclear how the driver ended up on the tracks and why the door of his cabin was open. "The driver apparently fell out due to his own carelessness," the spokesman for Moscow metro police, Alexei Myshlyayev, told the RIA Novosti news agency.

Myshlyayev said that security camera footage confirmed that no one else was in the driver's cabin at the time.

The Moscow metro, famed for its ornate stations with chandeliers and statues, is vital to the traffic-snarled capital, with ridership of more than nine million on working days.