A broken down train at City Thameslink is causing havoc across the entire network, with Thameslink warning services may be cancelled or delayed and that all trains will be "exceptionally busy".
National Rail said the broken down train cannot be moved without assistance from a rescue train.
"This has been arranged to allow both lines to reopen, however this will take some time as the trains have to move at a slow speed during the rescue," the rail operator added.
The following alterations will apply:
- Four trains an hour will run between Bedford and London St Pancras International calling at all stations.
- One train an hour will run between London Blackfriars (vice Luton) and Wimbledon via Sutton
- One train an hour will run between London Blackfriars (vice Luton) and Wimbledon via Mitcham
- Kentish Town to Sevenoaks will run as timetabled but terminate/start at London Blackfriars
There will be a significantly reduced service running during this mornings peak on routes between:
- Bedford and London
- London and Three Bridges
- Sutton and London via Wimbledon and Mitcham Junction
National Rail warned all services that are running will be exceptionally busy and passnegers may need to wait for a later train.