All Thameslink services have been cancelled or delayed due to damage to overhead electrics between St Pancras International and Blackfriars .
Commuters will be facing disruption for most of the morning, with "major disruption" predicted to last until at least 2pm due to blocked lines.
All services were cancelled earlier this morning.
The line have reopened but travellers are still facing having their trains cancelled or severely delayed.
A signal failure at Watford Junction had caused problems earlier on the London Overground, but Transport for London say that there are now only “minor delays” on the line to and from Euston.
Damage to overhead wires outside Blackfriars has also caused issues with Great Northern services.
A Thameslink spokesman said: “Due to multiple incidents at City Thameslink and Blackfriars, the power has been switched off to the line between St Pancras and Blackfriars in both directions.
“Trains are unable to run in either direction."
He added: "Thameslink advise you not to travel at this time as they cannot guarantee a train service through the following stations: London St Pancras International, Farringdon, City Thameslink and Blackfriars.”
Another rail company, Great Northern, has tweeted in reply to a customer: “We are experiencing severe congestion on the line due to damage to the overhead wires in London Blackfriars which results in late notice cancellation of services.”
Information about alternative travel options can be found here.
