Trains are unable to run due to flooding on the track.
Southern Rail made the announcement this morning at around 11.20am following heavy rainfall.
Trains are unable to run between Crowborough and Uckfield.
Rail replacement buses are in place between the stations.
A Southern Rail spokesman said: “Due to heavy rainfall on the railway, trains are unable to run between Crowborough and Uckfield.
“Network Rail are on site and attending to this flood. We're now waiting on confirmation to say that it is safe to run on this section again.
“Rail replacement buses will remain in place to ensure onward connections this afternoon.”