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, CNN reported.

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.

The outage took out lighting and power sockets, and caused subway systems to suddenly fail. In Madrid, traffic piled up on the roads after the lights went out.

“I was driving and suddenly there was no traffic lights … It was a bit of a jungle,” Luis Ibáñez Jiménez told CNN. “I saw a massive bus coming, and I had to accelerate a lot to go past it.”

The cause of the blackout was unclear, but its impact was dramatic: transport hubs were shuttered and governments in both countries, which share a population of around 60 million people, hastily arranged emergency meetings to co-ordinate a response, according to CNN.