Travellers watch the announcement boards in Euston rail station during the busy morning rush hour on August 09, 2019 in London, England. The train network was hit by major delays yesterday after all services out of London Euston were suspended due to a signal failure.

Most power is restored after outages affected a large area of London and the South East due to an issue on the national transmission network, National Grid said via tweet on Friday.

"By 18:30 all demand was restored by the Distribution Network Operators," the tweet said. "The system is operating normally."

@ng_eso: , allowing for power to be quickly restored. By 18:30 all demand was restored by the Distribution Network Operators. The system is operating normally. 3/3

The update came after UK Power Networks said the power cuts were due to an issue on the national transmission network.

@UKPowerNetworks: "This is due to an issue on the national transmission network which has impacted our customers," the tweet said, "We believe all supplies have been restored."

The UK Power Network's tweet followed its original tweet notifying customers of the power cuts.

"We believe this is due to a failure to National Grid's network, which is affecting our customers," the tweet said. "We may not be able to answer individual tweets at this time. Please keep an eye on our feed for updates."

@UKPowerNetworks: 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.

Western Power Distribution, an electricity distribution network operator for the Midlands, South West and Wales, said in a tweet it was experiencing a "major incident on the national electricity infrastructure."

"We are in the process of restoring customers now and will provide further updates as soon as possible for specific areas," the company said.

@wpduk: We are currently experiencing a major incident on the national electricity infrastructure. We are in the process of restoring customers now and will provide further updates as soon as possible for specific areas We are sorry for the inconvenience this is causing.

Train service was also disrupted, according to the National Rail.

@nationalrailenq: Power supply problems are currently causing disruption to a large number of train services. Information screens in some areas are also affected.