Footage of the incident in the city of Cameron, in Milam County, showed thick black smoke streaming across the sky.
Nearby homes had to be evacuated and at least one property was destroyed by fire, police said.
The vehicle's driver and the people on board the train escaped unharmed and no injuries have been reported.
"Luckily, everybody seems to be OK," Milam County Sheriff Chris White said on Tuesday, telling reporters that there was "no more threat at this point" and that the focus was "to put the fire out and clean the mess up".
Mr White said the train had been carrying "some hazardous material" in trucks near the back, and that a section had to be disconnected and moved away from the fire.
"By the grace of God we were saved on that one," he said, without providing further detail of the material he was referring to.
Along with the petrol, the train was also reportedly carrying coal.
Mr White said that multiple fire departments had been deployed to the scene, but that the blaze was too hot to reach when crews first arrived, adding that they hoped to extinguish the fire using "heavy foam".
He described the lorry which the train hit as an 18-wheel "flatbed" vehicle, and said there was no indication that it had been transporting anything at the time of the crash.
The emergency services were made aware of the incident at about 06:40 local time (12:40 GMT), police said.
Several properties in the area were evacuated as a precaution and some roads were blocked, while people were urged to avoid the location.
The cause of the collision, at what was described by police as a regular road crossing with barriers, is not yet clear.