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
Ulster rugby stars Paddy Jackson and Stuart Olding are to stand trial on charges of rape, a Belfast court has ruled.
The Syrian city of Raqqa has been liberated from Islamic State militants, a senior commander for a US-backed force has said.
Paranoid schizophrenic Jeffrey Barry stabbed Kamil Ahmad before removing his penis in the attack at his flat in Bristol last year.