Power supplies have been returning in Spain and Portugal after large parts, including the capitals Madrid and Lisbon, were hit by a huge outage on Monday.
Millions of people were caught up in the chaos after the mass blackout brought many areas to a standstill, with trains stopping, planes grounded, internet and mobile phone services cut, traffic lights and ATMs down, and some routine hospital operations suspended.
Spain's interior ministry declared a national emergency and the two countries' governments convened emergency cabinet meetings as officials tried to find out what caused the outage which started around 12.30pm (11.30am UK time).
About half the electricity supplies in Spain have now been restored by the grid operator, Prime Minister Pedro Sanchez said on Monday evening, adding the rest should be back by Tuesday.
In a televised address, Mr Sanchez said authorities have not yet worked out what had caused the blackout in the Iberian Peninsula and were not ruling anything out.
He asked the public to refrain from speculation, and urged people to call emergency services only if really necessary.
Portugal's grid operator Ren claimed the outage was caused by a fault in the Spanish electricity grid, related to a "rare atmospheric phenomenon".
Ren says that, due to extreme temperature variations in Spain, there were "anomalous oscillations" in very high-voltage lines.
It also says that given the complexity of the issue, it could take up to a week for the network to fully normalise again.
