Update at 1:13 a.m. ET:
Officials have started the process of notifying families, it was announced at a press conference, though it wasn't certain if everyone on the train had been accounted for. The number of injured transported to the hospital was increased to 65, but the number of dead remained at five.
Philadelphia Mayor Michael Nutter said some major work would have to wait until the morning, as operating some of the heavy machinery in the dark wouldn't be safe. The next press conference also likely will wait until late Wednesday morning, he said.
He also said he'd been in touch with the mayors of Washington and New York, the start and end points of the Amtrak train's trip. Pennsylvania Gov. Tom Wolf, who recently had arrived in Philadelphia, said the state was working to provide anything needed.
Nutter said the accident likely would halt Amtrak and other service through the rail corridor, one of the busiest in the country, for the rest of the week.
Update at 11:38 p.m. ET:
At least five people were killed in the crash, Philadelphia Mayor Michael Nutter said during a Tuesday night press conference. At least 53 injured were transported to area hospitals, including six critical injuries.
"It is an absolute disastrous mess," Nutter said of the wreckage. "Never seen anything like this in my life. ... We have train cars that are on their sides, ripped apart."
Mayor Nutter said there were a total of 243 people on the train, including five Amtrak employees. Amtrak has asked people looking for information on passengers to call 1-800-523-9101.
Nutter said 120 emergency personnel responded soon after the crash happened at about 9:38 p.m. ET, and a police official said about 200 police officers eventually responded. The first firefighters on the scene found two people under the train, an official told the Philadelphia Inquirer.
The mayor said the National Transportation Safety Board is responding, Amtrak officials are on the scene and that he has been in touch with Pennsylvania Gov. Tom Wolf.
Our original post continues:
A Washington, D.C., to New York Amtrak train has crashed and derailed in the Port Richmond area of Philadelphia, sending at least 22 passengers to local hospitals. Some cars appear to have rolled, and the train appears to have sustained serious damage.
Emma Jacobs, reporting for NPR, says Temple University Hospital and Jefferson University Hospital each have received at least 10 patients, while Hahnemann University Hospital has received two and is expecting more.
Amtrak has announced that all service tonight between New York and Philadelphia has been canceled; SEPTA regional train service between Philadelphia and Trenton is also canceled.
Former U.S. Rep. Patrick Murphy reported on Twitter that he was on the train — which The Associated Press reports was entering a curve at the time of the crash — and assisting injured passengers, and that he himself was unhurt.
Tom MacDonald of member station WHYY described the scene:
"The train is laying on its side; in some spots there are actually I-beams through the train ... there is definitely lots of damage."
MacDonald reports that firefighters are working to clear possible live wires from the wreckage.
Eight to 10 cars were involved in the derailment, and dozens of passengers may be injured, Fox News and NBC reported. MSNBC, citing Amtrak, reports there were about 240 people on board.
Passenger Beth Davidz told Fox News that some of the walking wounded were loaded into police wagons for transport to the hospital.
An AP manager who was on the train told the wire service that the crash was preceded by rapid deceleration, followed by violent shaking.