The Interior Ministry said the accident happened when several cars on a cargo train derailed and hit a passenger train moving on a parallel track near Naro-Fominsk, a town 50 kilometers (30 miles) southwest of Moscow. Officials said the accident was caused by a faulty track.
Footage from the crash site broadcast by Russian television showed one side of a passenger car torn away by the collision.
Nina Suslonova, the Moscow region's health care minister, told the Rossiya 24 news channel that five people were confirmed dead at the site. She said those who were injured were all from the same car.
The passenger train had been traveling from Moscow to Chisinau, Moldova.
Moscow's public transport department said the accident was caused by a crack in the rail.
Hundreds of rescuer workers, dozens of ambulance crews and several helicopters rushed to the site to help the victims. The emergency agency dealing with the accident said 15 of the injured were in grave condition.