Travellers are facing a nightmare this morning - with trains being stranded between Reading and Paddington after a Crossrail trial run is believed to have gone wrong.

Trains are unable to run between London Paddington and Slough or Heathrow Airport after overhead electric wires were "severely" damaged at Ealing on Tuesday night, causing chaos for commuters across Berkshire.

The accident is believed to have occurred around 10.30pm when a new Hitachi Rail class 802 test train torn down half a kilometre of cabling, immediately knocking out the power supply.

Trains already on the line had to be evacuated as many were carrying passengers to and from London.

Network Rail said it expected to open two of the four train lines by midday, but warned disruption would last until the end of the day and possible into tomorrow.

Great Western Railway (GWR) added that a reduced timetable would impact most mainline routes to and from Paddington.

The operator said: "Owing to the extent of the damage, no trains are expected to be able to operate between London Paddington and Hayes & Harlington in either direction for much of Wednesday.

"As a result, GWR, TfL Rail and Heathrow Express will not be operating a train service between London Paddington, Hayes & Harlington or Slough until such time as repairs have been completed."

It added: "If you are travelling from London beyond Reading please do not go to London Paddington but instead travel straight to either London Waterloo, London Marylebone or London Euston depending upon your ultimate destination."

Network Rail added its engineers are attempting to fix 200 metres of "damaged electric power cables" near Ealing after an outage which prompted chaos for commuters on the line into London Paddington.

Numerous passengers posted to social media complaining about delays on the line overnight and on Wednesday morning, including Param Dhaliwal who wrote: "No lights, air conditioning, toilet facilities or updates! When will passengers be evacuated from the train stranded between London Paddington and Acton Main line?"

Anila Babla tweeted: "Just got home 6hrs after I left Maidenhead thanks to no electrics into Paddington. @GWRHelp please advise re compensation! I'm sorry for the emergency guys who had to take all the flack with good humour."

A Network Rail spokeswoman said: "We are experiencing severe disruption on all services into and out of London Paddington and this is likely to affect services in other areas for the rest of the day.

"This is owing to 500 metres of extensive damage caused to overhead power lines in the Hanwell area yesterday evening. We have been working throughout the night to understand the extent of the damage and we are focusing on trying to open some lines into London Paddington as soon as possible.

"We will provide regular updates on our progress throughout the day as the extent of the damage becomes clearer.

"We apologise for the inconvenience this has caused passengers and we advise passengers to check before they travel. However, severe disruption is expected on most routes.

"Passengers travelling to London can travel to Waterloo via Reading and Marylebone via Oxford. A rail replacement bus service is currently operating between London Paddington and Heathrow Airport."