Metro trains were disrupted for more than an hour on Tuesday morning after a crack was detected in one of the tracks for south-bound trains at Central station.

“It was a small crack apparently caused by contraction of the rail following sharp changes in temperature. It’s a common phenomenon during summer,” said Protyush Ghosh, deputy general manager, Metro Rail. “Had the crack been unnoticed and the gap widened, there could have been a derailment.”

The crack was spotted at 10.20am, after a Kavi Subhash-bound train had left the station. “Services through the station was stopped immediately. Trains ran between Kavi Subhash and Maidan, and between Dum Dum and Girish Park stations till 11.30am, when normality resumed,” said an official.

Even after resumption of the service on the entire stretch, trains ran at a slower pace than usual till around 3pm. “A temporary clamp was placed on the track to prevent the crack from widening, which forced the trains to run slowly,” the official said.