A massive power outage has knocked out electricity across huge parts of Spain and Portugal, shutting off traffic lights and causing chaos at airports, train stations and on the roads.

Portugal’s grid operator Redes Energéticas Nacionais (REN) said electrical supply was lost across the entire Iberian Peninsula, and in parts of France, shortly after midday. Hours later, Spain’s Prime Minister Pedro Sanchez said authorities were still not sure what caused the blackout.

It may take a week for the network servicing both countries to be fully repaired. Meanwhile, millions are without power.