Specialist PSNI teams are carrying out searches at the railway line in Lurgan, Co Armagh between Lake Street and Kilwilkie Road.
It comes after police received intelligence reports of suspicious activity in the area.
In a statement, the PSNI said: “Police are currently carrying out a search at the Lake Street and Kilwilkie Road, Lurgan area.
“The search is in relation to a report of suspicious activity in the Kilwilkie area on Sunday 27 April. There are no further details at this stage.”
It has meant that Translink have to put on a bus substitution service Lisburn and Portadown until further notice.