Manchester Piccadilly was forced to close after protesters stormed the tracks causing many lines to be suspended in and out of the station.
Campaigners waving banners that read “Stop Turkey from helping ISIS terrorists” stormed the station concourse and sat down on the tracks causing train delays and cancellations.
Delays are expected to continue until at least 3pm National Rail said.
Rail bosses have warned passengers that many journeys may be affected by the protest and have advised travellers to check their journey before travelling.
A National Rail spokesman said: “A trespass incident at Manchester Piccadilly is causing disruption to trains at the stations.
“Trains may be amended, cancelled or delayed. “
Virgin Trains and Northern reported that all lines from the station were blocked.
One passenger travelling to Wigan told the Manchester Evening News that the station was “swarmed” by more than 100 protestors.
They said the campaigners were handing out leaflets to the public but that the protest “seemed pretty peaceful.”
British Transport Police said officers were responding to the incident at about 2pm on Sunday.
A spokesman said: "We were called to Manchester Piccadilly station shortly after 1pm on Sunday March 11 following reports of protesters trespassing on the tracks.
"The station has been closed to trains while officers at the scene work to ensure their safe removal and the reopening of the station."
