(CNN) [Latest developments]

11:46 p.m. ET: At least 49 people were hospitalized, including six who were critically wounded, authorities said.

11:41 p.m. ET: At least five people are dead, Philadelphia Mayor Michael Nutter said. Seven cars and engines in "disarray" -- turned over, upside down, he said. "It is an absolute, disastrous mess."

11:24 p.m. ET : There were approximately 238 passengers and 5 crew members on board, Amtrak said.

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