Trains are currently delayed between Haywards Heath, Brighton and Lewes.
According to Southern Rail, there is disruption between Haywards Heath and Brighton and Lewes due to a fault with the signalling system near Wivelsfield.
While this has been fixed and all lines have reopened, trains between these stations continue to be affected by delays.
Southern Rail said the service should be back to normal by 7.30pm this evening.
The fault happened with the points system. According to Southern, points are movable sections of track that allow trains to move from one section to another. In this case, they divert the track after Haywards Heath to either Brighton or Lewes.
When these fail, trains are unable to follow their intended path.