A CSX freight train derailed in Alexandria Saturday morning, and some of the derailed cars then damaged part of an overpass used by the train, according to a federal safety official.

Robert Sumwalt, chairman of the National Transportation Safety Board, said the train derailed about 7 a.m. in the 4300 block of Wheeler Avenue. Some of its derailed cars then damaged part of the overpass, he said.

No injuries were reported and none of the derailed cars appeared to carry any hazardous materials, authorities said.

The cause of the derailment was not immediately known, and the incident remained under investigation late Saturday.

However, Sumwalt said some of the ballast gravel that underlies the tracks near the point of the derailment had slid from its normal position. He said authorities would investigate whether this resulted from weather, or from some maintenance problem.

He said that the derailment occurred about a tenth of a mile from the overpass, but that the train cars continued on to the overpass.

Three parallel tracks run over the overpass. Rail service had been restored on two of them as of late Saturday, but at reduced speed, Sumwalt said.

CSX released a statement and declined to comment further at midday Saturday: “CSX is working closely with local firefighters and other first responders to assess the situation, and the safety of the community and everyone on site is our top priority as we develop a recovery plan.”

The three-locomotive train included 167 cars; 91 were loaded and 76 were empty, the statement says.Norfolk Southern is also on the scene assessing the effect on its tracks, a company spokeswoman said.

Fire officials were dispatched shortly after 7 a.m. Saturday and found a jumble of tracks and debris near Floyd Street and Wheeler Avenue, Dubé said.

This story has been updated