Trains may be delayed or cancelled due to a trespass incident between Eastbourne and Hastings.
Southern said the incident was disrupting services to Hastings.
According to Southern, the driver of the 8.01am Brighton to Ore service reported that they had to stop because of the trespasser who was on the line.
The driver of this train had to then check the area of the level crossing before continuing further. This train is now on the move, with a delay of approximately nine minutes. Some other trains are also being delayed in the area.
This problem was reported at 8.58am. Railway security staff were deployed shortly afterwards, and they are currently on their way to check the level crossing, Southern added.
A spokesman added: “Please be aware of minor delays and leave some extra time for any essential journeys. We have received information of a trespasser on the tracks at a level crossing near Pevensey Bay station, on the route between Eastbourne and Hastings.
“This will affect some Southern services to and from Hastings, Ore and Ashford International - both eastbound and westbound on the affected routes.”