Damage to overhead wires between London St Pancras International and London Blackfriars has meant all Thameslink lines are blocked.
“Train services running between these stations may be cancelled or delayed,” Thameslink has said in a statement.
Disruption between London St Pancras International and London Blackfriars is expected until 11am.
Disruption between London St Pancras International and St Albans is expected until 10am.
A speed restriction over defective track between West Hampstead Thameslink and St Albans is causing disruption to trains between these stations.
Trains may be delayed or cancelled, with disruption expected until 10am.
“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,” the company said.
“Trains are unable to run in either direction.”
Thameslink advises people not to travel at this time as they cannot guarantee a train service through 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.”