Trains between London Paddington and Heathrow terminals could be delayed by up to an hour due to the emergency services dealing with an incident between the stations.
The issue is also causing delays between Paddington and Slough.
National Rail has said lines have reopened but while the service recovers there may still be cancellations and 60-minute delays.
The issue is also causing severe delays on the Elizabeth line.
It comes after part of the District Line was forced to shut for around two hours after a car crashed through a fence and collided with a barrier just metres from the Tube track.
Meanwhile, Aslef train strikes have hit the capital’s transport network for a second day in a row.
Fewer London operators are affected on Wednesday but the Heathrow Express and London Northwestern Railway are among them.
On top of this, several of the London operators which saw walkouts on Tuesday are still struggling with delays.
These include Southern, South Western Railway and Thameslink which are expecting late starts or running revised timetables.
Meanwhile a “nationwide issue” with Border Force e-gates that caused chaos at airports across the country into the early hours of Wednesday has been resolved, the Home Office has announced.
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No service on Piccadilly Line after casualty on the track
There is no service between Acton Town and Hyde Park Corner on the Piccadilly Line while emergency services deal with a casualty on the track.
Trains delayed by 60 minutes between Paddington and Heathrow
Trains between London Paddington and Heathrow Terminals may be delayed by an hour due to the emergency services dealing with an incident.
The issue is also causing delays between Paddington and Slough.
National Rail has said lines have reopened but while the service recovers between the stations there may still be cancellations and 60 minute delays.
The issue is also causing severe delays on the Elizabeth Line.
Minor delays on the Elizabeth Line
There are currently minor delays between Paddington and Reading as well as to Heathrow terminals on the Elizabeth line.
The issue was caused by a trespasser on the track at Southall.
The Metropolitan Line is now running again but with severe delays following a faulty train at Farringdon.
Trains unable to run on the Metropolitan Line due to faulty train at Farringdon
There is currently no service between Aldgate and Baker Street on the Metropolitan Line while Transport for London fix a faulty train at Farringdon. The issue has also created severe delays on the Hammersmith and City Line and the Circle Line.
Disruption between Barnes Bridge and Hounslow until the end of the day
Some lines between Barnes and Barnes Bridge have been blocked due to a track circuit failure.
Trains are unable to run on the line between Barnes Bridge and Hounslow in the direction of Feltham.
Services are also running at a reduced speed between Mortlake and Barnes towards London Waterloo.
National Rail has warned of cancellations and delays.
Trains running again on the District Line
Transport for London has said trains are running again on the District Line.
Trains were unable to run for around two hours after a car crashed through a barrier near Southfields station shortly before 3pm.
TfL has warned there are still minor delays between Earl’s Court and Wimbledon due to the issue and further delays following a signal failure at Parsons Green. There is a good service on the rest of the line.
Driver 'suffered a medical episode' before car crashed through barrier near District Line
A driver is believed to have suffered a medical episode before their vehicle crashed through a barrier near Southfields station.
A spokesman for the British Transport Police said: “Officers were called to the line near Southfields underground station at around 2.55pm today (8 May) following reports that a car had gone through the fences alongside the railway line.
“Officers attended, alongside colleagues from the London Fire Brigade, Network Rail, and the Metropolitan Police Service and work is ongoing to clear any obstructions from the tracks.
“It is believed the driver of the vehicle suffered a medical episode and they have been treated by paramedics.”
Severe delays on London Overground at rush hour
There are severe delays on the London Overground at rush hour between Highbury and Islington and Stratford, Transport for London has warned.
The delays are being caused be a signal failure at Stratford.