It follows reports of a device being left on the line in Lurgan.
As a result, there is a large police operation ongoing this evening targeting serious crime in the Lurgan area.
Searches are being carried out in the Cornakinnegar Road.
The railway line has been closed between Lisburn and Portadown a bus substitution service is operating,
Senior police in Lurgan have thanked the local community for their patience and cooperation as the clearance and search operation continue.