CHAFFEE -- Burlington Northern Railroad employees believe a broken rail caused nine cars of a freight train to derail north of Chaffee early Thursday.

Lee Bollinger, track supervisor in Chaffee for Burlington Northern said Thursday afternoon it appeared that the severe cold weather had caused the track to become brittle and break under the weight of the 79-car freight train passing through the Chaffee area at about 8 a.m.

But Burlington Northern officials say they are continuing to investigate the derailment.

There were no injuries reported in the incident.

Train workers expected to have the track repaired and back on line by midnight Thursday.

Four hopper cars loaded with mineral ore and two cars loaded with rolls of paper derailed; the other three cars were empty. Bollinger said that some of the derailed cars struck two empty cars sitting on a nearby track, damaging them slightly.

The 5,000-foot-long train was southbound on the main railway line when the nine cars derailed, just north of the Chaffee city limits.