The airline TAP Air Portugal has urged passengers intending to fly from Lisbon to avoid the city's airport until further notice. Portugal and Spain were hit by widespread blackouts on Monday, leaving millions without electricity.

The power outrage caused chaos and mayhem in cities in both countries and brought traffic in Madrid and Lisbon to a virtual standstill. Spain's entire rail network shut down, while airports were forced to cancel flights.

Officials in Lisbon said operations were "limited" at the capital city's airport.

However, TAP strongly advised passengers against making their way to the airport until further notice.

In a statement on Facebook, they wrote: "Due to the power cut in several European countries, the operation of airports is temporarily very limited.

"TAP requests that you do not go to the airport until further information."

In Spain air traffic was reported by the news outlet ABC to be operating at "half capacity".

Spanish airport operator Aena confirmed that Madrid's Barajas Airport had been hit the hardest, with flight cancellations and delays.

Portuguese police said traffic lights were down and that the metro systems in Lisbon and Porto were closed.

There were also reports of long queues at cash points, as people tried to withdraw money in the panic.

The country's electricity operator said the power cut was caused by "rare" atmospheric phenomenon, related to variations in temperatures.

Both Portugal's Prime Minister Luis Montenegro and the president of the EU Council Antonio Costa said there was as yet no indication that the outrage was caused by a cyber attack.

The power failure has also led to the postponement of matches at the Madrid Open.

Organiser said that "in order to guarantee general safety, the nationwide power-cut experienced in Spain on Monday 28 April has forced the cancellation of both the day and night sessions at the Mutua Madrid Open".