A freight train derailed and collided with a passenger train south-west of Moscow, killing at least six people and leaving 45 others injured, officials said.
Carriages on the goods train were derailed in the crash, which happened at 12:38 (08:38 GMT) near the town of Naro-Fominsk, about 50 miles southwest of Moscow, as the passenger train was travelling from the Russian capital to Moldova's capital Chisinau, BBC News reported.
Emergency services reportedly carried injured people from the train after rushing to the scene.
While five people were killed at the scene, a sixth victim died in a hospital. Another 45 people were injured, 25 of whom were taken to hospital for treatment.
The passenger train, which was reportedly carrying about 400 people, was hit after several carriages on the goods train came off the rails near the town of Naro-Fominsk, officials said.
Rescue coordinator Vadim Andronov told Russian news agency Itar-Tass that the death toll was likely to rise, BBC News reported.
"One of the carriages of the passenger train was crushed by the freight train wagons. Rescuers are working to pull out injured people being crushed by the wagon," he said.
Rescue crews and medical teams were doing everything they could to save lives, Oleg Salagay, a spokesman for the health ministry, said.
"Medics are working at the scene now, assessing the condition of the injured," he said.
"All the necessary medical aid is being provided for them, and this gives us hope for a successful outcome."
The cause of the accident was not immediately known. Investigators were on site and officials said a criminal probe had been launched, Agence France-Presse reported.
"We tried to use an emergency brake. We couldn't see anything ahead, there was lots of dust," one of the drivers of the passenger train was quoted as saying by RIA news agency.
Traffic on the line - which also serves Kiev in Ukraine - was suspended as a result.
