The loco pilot of the Mumbai-Thiruvananthapuram Express, which ran over the slab, informed police and railway authorities after stopping the train at the next station, police said.
The slab was placed across the track between Eravipuram and Mayyanad stations, about 8 km from here, they said adding it broke into pieces as the train ran over it.
Police have begun an investigation and said the possibility of a sabotage attempt could not be immediately ruled out as anti-social elements often gathered at the spot during the nights.
