Trains have been delayed or cancelled because of a trespasser on a track.
Services were suspended on the route between Huyton and Earlestown in Merseyside following the incident earlier.
The line has since reopened but services between Liverpool and Manchester were still set to be cancelled and delayed, with disruption expected to last until 11:00 BST.
British Transport Police said officers arrested a man on suspicion of trespass and obstruction of the railway at Newton-le-Willows at about 06:15 BST.