Spain and Portugal are reeling from a massive, unexplained power outage that knocked out traffic lights, caused chaos on roads and in airports, and prompted both countries to declare a state of emergency.

Officials are yet to confirm exactly what caused more than 50 million people to lose power this afternoon, with a number of potential explanations having been offered in the panic

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