The derailment occurred shortly after midnight local time about 20 miles west of Dodge City, Kansas, Amtrak said in a statement.
"The condition of the track really is going to be the focus of the investigation," National Transportation Safety Board member Earl Weener said today at a press briefing. "There is every indication that the train was being updated properly."
The NTSB said the train was likely traveling at about 60 mph, the speed limit for that corridor, when an engineer noticed something was wrong with the track and pulled the emergency break. The possible defect was likely the result of changing weather, a government official briefed on the investigation told ABC News.
The actions of the engineer averted a far worse accident, according to the NTSB, and Weener told reporters the worker was "quite vigilant" by noticing the possible defect.
The track in the rural area of Kansas where the derailment took place is inspected twice a week and the most recent inspections have met federal standards, a BNSF spokesman said. The track was inspected as recently as last Thursday, the NTSB said.
Of at least 32 injured passengers taken to hospitals in rural Kansas, 29 were discharged later this morning, with two reported in critical condition. An earlier statement from the Gray County, Kansas, Sheriff’s Department said one person was transported from the scene of the crash to a hospital by helicopter.
One Amtrak crew member suffered an injury on the train and was treated at the scene, and not sent to the hospital.
Seven of the train's nine cars derailed, according to the Gray County Sheriff's Department.
Last May, an Amtrak train derailed near Philadelphia, killing eight people and seriously injuring dozens of others when it went faster than the recommended speed around a curve.