SAN ANTONIO (AP) — Officials say 21 freight cars hauling coal from Wyoming have derailed in South Texas during searing heat that reached 100 degrees (38 Celsius).

Union Pacific spokesman Jeff DeGraff says authorities are investigating whether heat played a role in the derailment late Sunday afternoon in San Antonio. He says heat can cause rails to buckle.

DeGraff says nobody was hurt. The train carried two crew members. One locomotive also derailed.

DeGraff says no hazardous materials were aboard the 150-car train hauling coal from Wyoming fields to the San Antonio area. DeGraff says some coal spilled as a number of cars piled into each other. Several cars overturned.

Cleanup continued Monday. DeGraff says the derailment happened on a section of track off the main line so rail traffic was not impeded.