Photos have emerged of a train which derailed at West Ealing on Tuesday morning (November 27) - causing "chaos" on west London's rail network.
National Rail described the delays as "major disruption" at a number of stations, including London Paddington, following the derailment.
While scores of passengers spoke of "chaos" at Paddington and beyond.
Work is ongoing to remove the derailed train from the tracks.
Photos uploaded to Twitter by Network Rail show engineers at the scene.
Follow live updates on the travel problems
Network Rail tweeted just before 9am: "Our engineers are on site at West Ealing as they work to clear a derailed train.
"Lines are open however some services are likely to be delayed or cancelled. Please do check before you travel.
"Thank you for your patience whilst we work to move the derailed train."
A Network Rail spokesperson also told this website: "Owing to a derailed train in West Ealing passengers are advised to check before they travel as some services may be delayed or cancelled.
"Our engineers are on site and will clear the derailed train as soon as possible."
The Network Rail photos confirm the derailed train was a Great Western Railway (GWR) service.
GWR have been telling customers on Twitter that the train was empty and that an investigation is underway into what happened.
We have contacted GWR for comment.
Perfect storm leads to huge queues and rush hour chaos
The delays caused by the derailed train at West Ealing follow earlier disruption because of a fire near the tracks in Southall.
The blaze, close to Heathrow airport, led to hold ups for passengers trying to use TfL and Heathrow Express services.
But the really chaotic scenes did not start until the delays from the fire and the derailed train at West Ealing combined.
At around 7.30am Twitter user @FredCoolBreeze shared his photos with this website of the huge queues packed onto platforms at Southall station.
He said he was behind the train that derailed.
You can see his photos in our gallery below:
Delays until at least midday
National Rail have extended the time disruption is expected to continue until.
As of 9.30am, their advice was that delays would continue until 12pm.
A statement on the National Rail website said: "The operational incident at West Ealing has now been dealt with and service recovery is underway.
"However, whilst services recover, trains between Slough / Heathrow Airport and London Paddington may still be cancelled or delayed by up to 45 minutes.
"Disruption is expected until 12:00."
Advice for customers from National Rail
The Heathrow Terminal 4 service has been suspended during the disruption.
Great Western Railway customers are advised that they may use tickets on the London Underground and London Buses via any reasonable route, according to National Rail.
While TfL customers have been told they can use tickets on any of the follow services:
- Great Western Railway between Hayes & Harlington and London Paddington
- London Underground between Heathrow Terminal 4 and London Paddington
- London Buses route 140 between Heathrow (Bus Station) / Heathrow Terminal 4 and Hayes & Harlington
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