"All trains at the station will remain until the station opens".
Hours earlier pro-Kurdish demonstrators jumped onto the tracks at Manchester Piccadilly station, forcing the station to shut.
Officers used batons to hold back the crowd.
All lines in an out of the station have been suspended as a result of the demo, which began around 1pm.
Hours later, King's Cross was closed after dozens of protesters gathered outside.
The protest at Manchester Piccadilly forced the cancellation of a number of services, while others had delays of up to 90 minutes.More news: Prince William may 'walk Meghan Markle down the aisle' at Royal Wedding
More news: Rice Midstream Partners (RMP) Lowered to Market Perform at Wells Fargo & Co
More news: Forget The Rockets, Stephen Curry's Ankle Is The Warriors' Biggest Problem
Manchester's main railway station has been closed after anti-Turkey protesters climbed on to the tracks leaving airport-bound travellers stranded.
A spokesman for the Manchester branch of the Friends of Kurdistan solidarity group said about 400 people had gathered in the city for an global day of action in defence of Afrin.
Turkey launched a solo military offensive against the Syrian Kurdish People's Protection Units or YPG two months ago to clear them from Afrin in north-western Syria - something described as ethnic cleansing by those sympathetic to the Kurds. "It's an attempt to break the silence and raise the issue in people's consciousness".
British Transport Police superintendent Mark Cleland said the force respected "the right to peaceful protest", but said those who stormed the tracks at Manchester Piccadilly "will be subject to intense investigation with a view to arrest and prosecution".
A spokesman for Network Rail said: "The station will remain closed until all protesters have been removed".