Emergency services are attending at a major incident at the Smithy Bridge level crossing in Littleborough.
Crews were scrambled to the scene in Rochdale at around 7pm on Monday.
It has not yet been confirmed what has happened.
British Transport Police has been contacted for a comment.
One commuter who was at the scene tweeted: "I'm on this train and I can see how well your staff are dealing with such a difficult situation."
Train lines are currently blocked between Rochdale and Todmorden.
Read more of today's top stories here
Bargain Booze worker fights with knife robber during raid in Wigan
Landlord and another man seriously injured after stabbing at Salford pub
A number of services have been cancelled between these stations.
Northern Rail say delays of up to an hour can be expected until at least 10pm.
Passengers have been advised to use the Metrolink or coaches that have been put on at Rochdale, Hebden Bridge and Todmorden.
It is thought that Smithy Bridge Road has also been closed.
