The railway line between Manchester Oxford Road and Liverpool Lime Street is currently blocked due to trespassers.
Passengers are being warned services between the two stations could be cancelled or delayed by up to 30 minutes.
According to Northern, the disruption is expected to last until 8.15am.
British Transport Police have been called to the incident.
It is unknown how many people are on the tracks at this stage.
A statement posted on the Northern website said: "Due to trespassers on the railway, trains are currently not able to call at stations between Liverpool Lime Street and Manchester Oxford Road.
"British Transport Police are en route."
Passengers are being advised to check information screens and listen to customer announcements for updates.