Police were called to Eccles train station this afternoon after a trespasser walked onto the line.
No-one is thought to have been hurt.
Northern Rail tweeted that services may be delayed this afternoon and into rush hour.
NEW: Due to a trespass incident at #Eccles services running through this station may be delayed
— Northern Rail (@northernrailorg) August 27, 2015
Trains between Liverpool Lime Street and Manchester Airport are being terminated by Manchester Piccadilly, with some Northern Rail services running express.
Transpennine Express report that a train is awaiting a replacement driver at Eccles and should be on the move soon.
There are also delays of around 45 minutes between Wigan North Western/Liverpool Lime Street and Manchester Oxford Road/ Manchester Victoria expected until 5.30pm tonight, Thursday 27 August.