Emergency repairs to the track between East and South Croydon stations are causing significant disruption to trains running between these stations.
As a result, trains may be canceled, delayed by up to 20 minutes, or service changes may occur.
JNR confirmed that disruptions are expected until 4 p.m.
Affected rail companies include Gatwick Express, Southern and Thameslink, with a wide range of routes affected.
The Gatwick Express and southern services between London Victoria and Reigate will be suspended until further notice.
Passengers traveling between Redhill and Reigate can travel on Great Western Rail services at no extra charge, as well as use their tickets on alternative Southern or Thameslink services between Redhill and London.
“If you travel through South Croydon, you may need to change trains or take an alternative route to your destination, adding up to 20 minutes to your journey time.”