Quick thinking may have averted a train crash in South Canterbury.

A passerby spotted a badly buckled line near Waimate on Tuesday morning and called 111.

The South Communications Centre dispatcher asked for details, but the man was quick to point out there was no time as the train could be on its way.

Centre Inspector Kieren Kortegast says it is not common practice but the dispatcher transferred the caller directly to train control and the train stopped just six metres short of the buckled track.

Inspector Kortegast says it is very likely the train would have crashed but for the quick actions of the passerby, the police and train control.