Large parts of London and Britain came to a standstill after a fault on the National Grid halted trains, tubes and traffic lights.

The disruptive power outage brought chaos to the nation at the start of Friday evening’s rush hour, with hordes of frustrated commuters unable to move.

Millions of people were affected by blackouts reported across England’s South East, South West and North East as well as the Midlands and Wales.

Clapham Junction apocalypse 👻 #powercut pic.twitter.com/yfJwoYeI3I

— Maddie Hampson ✨ (@MaddieHampson_) August 9, 2019

Services in and out of London were cancelled or delayed while trains drew to a stop mid-route after losing power, with passengers trapped on sweltering trains or forced to walk the tracks to safety.

16:38 from Highbury and islington get well soon. Driver handled it well ! #powercut @GNRailUK pic.twitter.com/ZkIEzlYKGr

— George (@georgeykeogh) August 9, 2019

Passengers eager to get home after a long week described apocalyptic scenes and mayhem, with people trapped in darkness not knowing what was happening.

Departure boards at busy stations like Kings Cross went blank at the height of the outage while on the roads, driver confusion set in when traffic lights stopped working.

There were reports of a 15-minute outage at Newcastle Airport but flights were not affected while Heathrow, Gatwick and Luton airports said they had not been affected.

No more trains on the board at kings cross! #powercut pic.twitter.com/RwpAgW4AbL

— Dr Soraya M (@DrSorayaM) August 9, 2019

National Rail Enquiries confirmed most trains were at a standstill in  London and the South East at what is one of the busiest times of the week.

About a million people were also plunged into darkness while offices and businesses went black and commuters were forced to use their phones as torches in dark tunnels and stations.

Police scrambled to manage the chaos, with officers deployed to busy traffic intersections were lights were on the blink and taking charge at railway stations.

The so-called Black Friday power meltdown was blamed on a “large scale National Grid failure” caused by problems at two power generators.

Power was eventually restored after hours of disruption on rail networks however rail authorities warned travellers that delays would continue.

Lovely start to the #weekend #powercut @NetworkRailEUS pic.twitter.com/jtdI9sC9Wy

— PradumnPamidighantam (@PradumnP) August 9, 2019

Power companies blamed the outage on the National Grid, a multinational company which owns and maintains the high-voltage electricity transmissions in England and Wales.

National Grid head of national control Julian Leslie explained the outage in a Twitter video:

“Earlier this evening we had an unplanned, near-simultaneous event on our network,” he said.

“This event was the loss of two generators that connect to the National Grid transmission network in order to export our power.

“As a result of this and this rare event, the system needs to protect itself and what was happening was the frequency was falling – the system can see this – and unfortunately the way the system protects itself is by losing some demand.

“You would have seen this in the temporary and short power cut and since this happened at around five o’clock the distribution network operators have been working to restore your supplies to your home and your businesses.

“I’ve just had confirmation that all of the country’s supplies are now back on and the system is operating as normal.”

Julian Leslie, Head of National Control at National Grid ESO, explains more: pic.twitter.com/Tt1RiKhwRS

— National Grid ESO (@NationalGridESO) August 9, 2019

Earlier UK Power Networks tweeted that the outages affected “large parts of London and the South East”.

“We’re aware of a power cut affecting a large area of London and South East,” the tweet said.

“We believe this is due to a failure to National Grid’s network, which is affecting our customers.”

We're aware of a power cut affecting a large area of London and South East. We believe this is due to a failure to National Grid's network, which is affecting our customers. We may not be able to answer individual tweets at this time. Please keep an eye on our feed for updates.

— UK Power Networks (@UKPowerNetworks) August 9, 2019

The outage occurred on the same day Britain’s new Chancellor Sajid Javid met National Grid trainees.

A significant drop in generation this afternoon caused a major drop in frequency leading to power cuts across the country. Our fleet responded as expected helping stabilise the grid. Upside Energy Ltd #powercut @upsideenergy pic.twitter.com/k3RFRV9Blw

— Devrim Celal (@dcelal) August 9, 2019

Harriet Jackson, 26, told the BCC there was an “apocalyptic” scene on Northcote Road, in Battersea, when traffic lights cut out and cars were not stopping.

“Given it’s a Friday afternoon, it’s the last thing you want to encounter,” she said.

No trains in or out of London’s Clapham Junction Station. Photo: AAP