Spain's National Security Council held an extraordinary meeting on Monday after a huge power outage, allegedly caused by rare atmospheric conditions, brought much of the country and neighboring Portugal to a standstill.

Some parts of France also experienced brief disruption after power was lost around midday.

The Euronews website quoted Spain's national grid supplier Red Electrica as saying that around 12.30 pm local time, electricity consumption across the country halved from its usual level, suggesting there had been what it called an "exceptional and completely extraordinary" blackout.

By mid-afternoon, the process of reconnecting power supplies across Spain had begun, but there was a warning it could take up to 10 hours for everyone to have services restored. In Portugal, it has been suggested it could take days for normal service to resume.

No formal explanation has been offered yet, but the BBC quoted an official from Portuguese energy company Rede Eletrica Nacional, or REN, as blaming "extreme temperature variations in the interior of Spain" that had caused "anomalous oscillations in the very high voltage lines", although there has been no comment from Spain on this suggestion.

Telecommunications were badly affected as network coverage went down, and Madrid's Barajas International Airport and Humberto Delgado Airport in the Portuguese capital Lisbon were both forced to close, having knock-on effects for passengers all across the continent.

Trains were stuck in tunnels and city metro networks were shut, as residents of the Spanish capital Madrid were advised to stay at home and avoid any unnecessary journeys.

The international power loss took place just days after numerous heads of government and world leaders had been in London for an international summit on energy security.

European Council President Antonio Costa said he had been in touch with Spain's Prime Minister Pedro Sanchez and his counterpart in Portugal, Luis Montenegro, about the situation, and there was no reason to think that the incident had been caused by a cyberattack.

[email protected]