(Reuters) - A freight train derailed in Pittsburgh on Thursday and emergency crews were called, but there were no injuries and no hazardous materials involved, a railway spokesman said.

Investigators were still trying to determine how the Allegheny Valley Railroad train went off the tracks on Thursday morning, a spokesman for Carload Express, which owns the railroad, told Reuters.

About 10 train cars derailed when the train was negotiating a curve in the tracks, local media reported.

Pittsburgh is on the opposite end of Pennsylvania from Philadelphia, where an Amtrak train derailed on Tuesday night, resulting in seven deaths and scores of injuries.

(Reporting by Emily Stephenson in Washington and Barbara Goldberg in New York; Editing by Susan Heavey and Lisa Lambert)