Overrunning engineering works between East Croydon and South Croydon are bringing delays, disruption and cancellations to commuters from Brighton and Hove.
At least two trains have been cancelled and others have been held up by the works which are affecting almost the entire Southern network.
Southern said: “Due to overrunning Network Rail engineering work between East Croydon to South Croydon one line is closed for the day and platform 6 at East Croydon is also closed.
“A number of Southern and Thameslink services are subject to alteration and may be running from a different platform at East Croydon.”
Southern said that some delays could be expected until the end of services today.