Campaigners waving flags gathered on the tracks in a protest in response to Turkey’s war on Syrian Kurds.
Some protesters held a banner reading: “Stop Turkey from helping Isis terrorists.”
British Transport Police were called to the scene.
A BTP spokesperson said: “We were called to Manchester Piccadilly station shortly after 1pm on Sunday following reports of protesters trespassing on the tracks.
“The station has been closed while officers at the scene work to ensure their safe removal and the reopening of the station.”
National Rail said: “A trespass incident at Manchester Piccadilly is causing major disruption to trains at the station.
“Trains may be amended, cancelled or delayed by up to 60 minutes.”
British Transport Police said all protesters were safely removed from the tracks and the station had reopened.
Friends of Kurdistan Manchester, a solidarity group, said around 400 protesters gathered in an international day of action in defence of Afrin in north-west Syria, where Turkey launched a military offensive against the Syrian Kurdish People’s Protection Units or YPG two months ago.
Turkey’s intent to clear them from the area has been described as ethnic cleansing by those sympathetic to the Kurds.
Turkish attack on Afrin, northern Syria – in pictures
A spokesman for Friends of Kurdistan Manchester told The Independent: “Today is an international day of action in defence of Afrin, a canton in the north of Syria which has been under attack by Turkey for six weeks, alongside its allies in the Free Syrian Army.
“They have been using air strikes and ground troops against civilians. There have been hundreds of civilian casualties and documentation of war crimes.
They added: “This is an international day of protest to break the silence of the international community which hasn’t put any pressure on Turkey to stop what it is doing.
“It’s an attempt to break the silence and raise the issue in people’s consciousness.
“It was a sign of people’s frustration that the British government aren’t taking this seriously and are letting a potential genocide take place.”