The Metropolitan Transportation Authority said four or five carriages on the seven-carriages derailed close to the Spuyten Duyvil station in the Bronx, New York.
None of the cars entered the Hudson or Harlem rivers, which are adjacent.
Early reports indicate that four people have died and a further 48 are injured. This figure is expected to change.
More top news
Beyonce, Coldplay and Bruno Mars performed a medley of their hits during a powerful half-time performance at Super Bowl 50.
A doggy intelligence test may hold the key to a better understanding of human health problems like dementia, scientists say.
The Duchess says that children should be "supported through difficult times in their lives" at the start of Children's Mental Health Week.