They said track maintenance workers noticed the one-foot crack today and were repairing it.
Consequently, the Chennai-Rameswaram express was stopped at Mandapam, they said, adding it would be allowed to proceed to its onward destination after completion of works.
The cantilever Pamban bridge is the second longest in India after the Vembanad bridge at Kochi in Kerala.
On January 14, 2013, the bridge had suffered some damage when a barge rammed into a pier after its anchor gave way. It was later towed to safety and the damaged portion repaired.