Rail lines between Haywards Heath and Brighton are closed until further notice after a person was hit by a train.
There are currently no trains running between Brighton and London as a result.
The condition of the individual is not yet known.
Disruption is expected to last until at least 9pm tonight.
Network Rail are working with the emergency services to restore the railway.
Rail tickets are being accepted on Great Western and Southeastern trains.
Note, this is a separate incident to the earlier collision near Billingshurst.
More to follow.