Metro Railway CPRO R N Mahapatra told PTI that the snag developed at 11.25 am as the train entered the tunnel after leaving Park Street.
He said that all the passengers were evacuated from both sides of the rake by ladders which went down to the tracks.
Normal services were disrupted since then. The railway authorities ran truncated services from Dum Dum to Central on one side and Mahanayak Uttamkumar (Tollygunge) to Kavi Subhas (New Garia) on the other.