Railway services in and out of London’s Paddington station have returned to “near-normal” but the Heathrow Express is running at half capacity after damage to overhead electric cables caused severe disruption on Wednesday.

Network Rail said engineers worked overnight to make safe all four lines between Reading and Paddington. New overhead lines were installed but only one of the four lines to the station had electric power by Thursday morning.

👷👷‍♀️ Incredible effort throughout last night to repair such a huge stretch of damage to the overhead electric power lines between Reading and London Paddington.



🎥 This clip shows the team hard at work to ensure a virtually full service is in operation today. pic.twitter.com/roiYVrzkOd — Network Rail Western (@networkrailwest) October 18, 2018

Greater Western Railway said there were fewer than usual electric trains but most have been temporarily replaced by diesel trains.

Heathrow Express is running half as many services as usual, with two trains per hour instead of four.

Good Morning, ^HV here to assist with your journey today. Services will depart every 30 minutes.



London Paddington to Heathrow Airport - Services depart at 25 & 55 minutes past the hour



Heathrow Terminal 5 to London Paddington - Services depart at 12 & 42 minutes past the hour — Heathrow Express (@HeathrowExpress) October 18, 2018

Paddington, which is one of the UK’s busiest stations with about 100,000 passengers each day, was deserted for much of Wednesday after services on most key routes were suspended.

Trains were unable to run between London and Slough or Heathrow airport after 500 metres of overhead power cables suffered extensive damage during the testing of a new train fleet at Ealing at about 10pm on Tuesday.

In the early hours, National Rail said a near-normal service had resumed, with some alterations on commuter services in the Thames Valley area, including trains serving Maidenhead and Twyford.

Two of the four lines from Paddington were opened at about 12.40pm on Wednesday after engineers cleared debris and restored power so trapped trains could be moved.

The damage was caused by a high-speed Class 802 Hitachi train which was being tested between London and Bristol before its handover to GWR.

Hitachi said a “full and thorough” investigation would take place to identify the cause of the issue.

Class 802 trains are bi-mode, meaning they can operate on electric and diesel power. They take electricity from overhead wires using pantographs mounted on their roofs.

GWR is investing £500m in the new fleet delivered by Hitachi which will replace the operator’s high-speed rolling stock by the end of next year.