Two separate points failures on the railway line between Haywards Heath and Brighton are causing heavy train disruption this morning.
According to Southern Rail, Network Rail specialist engineers are on site at Preston Park working to fix a fault with the signalling system 'as quickly and safely as possible, so trains can run as normal'.
A Southern spokesman said: "Whilst this is ongoing services will not be able to use platform 2. This will impact on our services leaving Brighton this morning by causing delays of up to 30 minutes with late notice alterations and cancellation may occur."
In addition to this, Southern said it has been advised of a signal failure 'just south of Haywards Heath station in the direction towards London'.
"While this is ongoing trains have to be 'talked past'," the spokesman said.
All northbound lines had been blocked but have since been re-opened.
Southern tweeted: "All lines have re-opened, services will continue to be heavily delayed between Brighton and Haywards Heath."
Disruption is expected until 12pm.