Manchester Piccadilly railway station has been closed after protesters stormed the railway lines.
Campaigners are blocking the tracks and some have tried to climb overhead line equipment, National Rail said.
Crowds of people are holding banners which read “stop Turkey from helping ISIS terrorists”.
Virgin Trains said services running to and from the station may be cancelled, delayed or terminated until further notice.
A National Rail statement said: “A trespass incident at Manchester Piccadilly is causing disruption to trains at the stations.
“Trains may be amended, cancelled or delayed.”
It said “major disruption” is expected until 16:30 BST.
British Transport Police are at the scene. Officers were called to the station shortly after 13:00.
A spokesman said: “The station has been closed to trains while officers at the scene work to ensure their (protesters) safe removal and the reopening of the station.”