The crew of a toxin-laden train that crashed in Ohio tried to slow it down before it derailed, according to a preliminary report.
Federal investigators said the crew was alerted about an overheating wheel bearing shortly before the incident.
The 3 February derailment in East Palestine led to the release of toxic chemicals.
Transportation Secretary Pete Buttigieg was in the town on Thursday.
A total of 38 cars derailed in the crash, 11 of which were carrying hazardous materials. Residents later reported feeling unwell, as well as fish and wildlife dying.
The preliminary report from the National Transportation Safety Board (NTSB) found that a wheel bearing on the train had heated up over several miles before the incident.
Shortly before the derailment, it reached a "threshold" level of 253F (122C) above the normal temperature, the report said.
As the engineer applied the brakes to the train, an automatic braking system was also initiated, allowing the train to stop and response efforts to begin, according to the NTSB.
"After the train stopped, the crew observed fire and smoke," the report said.
The report, however, provided few details as to what exactly caused the derailment and how effective - or not - the response was.
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Fires at the derailment were contained by 5 February, but authorities remained concerned that five cars carrying 115,580 gallons (437,500 litres) of vinyl chloride - a odourless gas used to make PVC - might explode.
Authorities then conducted a controlled burn of the substance, sending a huge plume of black smoke over the small town of East Palestine.
The report - which is not final - also found no evidence that the train was traveling above the speed limit of 50mph (80kph).
The NTSB said that its probe is ongoing and that investigators will focus on the wheels and tank car design, as well as on the burning of the vinyl chloride and accident response.
In a statement published Wednesday, the Transportation Communications Union - which represents railroad workers - said it believes the crash may be partly the result of rail companies prioritising profits of safety.
"Somehow, 'we tried to warn you' just doesn't quite cut it," the statement said.
"For the past several years, rail labour unions - ourselves included - have been ringing the alarm bells about the dangers of the cost-cutting business model."
The release of the NTSB report comes on the same day as US Transportation Secretary Pete Buttigieg visited East Palestine to meet with residents and investigators.