On the video and images from the derailing site, smoke can be seen rising in the morning sky under the flames, where part of the bridge collapsed.
According to the Tempe Fire Department, the train was hunting unknown hazardous material.
Tempe Police Department Police Chief Sylvia Moir via Twitter urged residents to stay away from the scene, which she described as very dangerous.
Fire Department spokesman Brandon Siebert said officers were “taking precautions” and keeping firefighters and spectators “as far as possible” until they learned more about the hazardous material on the train.
According to Seibert, the operator is safe and helpful in helping hazardous technicians to determine what was on the train.
“It is possible that the partial bridge collapsed due to derailment, but it is not known that for this time,” Seibert said.
About 100 firefighters from Phoenix, Tempe, Chandler, Mesa and Scottsdale responded to the scene, according to Seibert.