An Amtrak train that derailed Tuesday, killing at least seven and sending 200 to area hospitals was traveling at twice the posted speed limit for the curve where the accident occurred. 

But it isn't clear that speed alone was the sole factor in the crash, said Robert Sumwalt, a member of the National Transportation Safety Board.  

At least 23 people remain hospitalized at Temple University Hospital -- eight of them critically -- after the New York City-bound Northeast Regional train went off the tracks went off the tracks Tuesday at about 9:30 p.m.

Sumwalt said at a news conference Wednesday that the engineer applied an emergency brake while the train traveled at 106 mph. Seconds later, the train, with seven cars and one engine, slowed to 102 mph. At that point the locomotive's black box data recorder cut out. 

The posted speed limit on the curve where the train derailed is 50 mph, though the track in front of the curve is rated for 80 mph. The engineer applied the break while the train was in the curve, Sumwalt said. 

Sumwalt's briefing marked the very beginning of what could be a lengthy probe into the derailment. Investigators will be looking into whether the condition of the track, the maintenance of the train, and the function of signals played any role in the accident. 

Meanwhile, officials are marveling that more people on the train, carrying 243 people, weren't killed.  

"To see these cars, these huge metal vehicles turned upside down, one basically almost split in half, most of the cars upside down, on their side or tilting, the engine separated, you know, this is a completely devastating situation," Nutter said. “It is incredible that so many people walked away from that scene last night."

Many of those injured were transported to Temple University Hospital, where chief medical officer Dr. Herbert Cushing said dozens of health care providers were pressed into service. 

Cushing told reporters Wednesday afternoon that doctors were seeing lots of rib fractures, and surprisingly few head injuries. 

Those rib fractures were a sign, Cushing said, that passengers and their belongings "rattled around in the train car a lot." 

Six of the dead were found at the site, among them Justin Zemser, 20, a cadet in the U.S. Naval Academy who was heading home to family in Rockaway Beach, New York. 

Also killed was Jim Gaines, 49, of Princeton, NJ and father of two. He was an employee of the Associated Press, where he worked as a video software architect. He died at Temple University Hospital. 

Cushing said he expected all of those who are hospitalized to survive. 

Philly tech CEO Rachel Jacobs, 39, who was reported missing earlier in the day was among those who died, the New York Times reported. 

It's unclear if the death toll will rise. Officials caution that many more are missing, and they continue to search the wreckage. Searchers do not know if some simply walked away from the crash in did not contact authorities.