Spanish Prime Minister Pedro Sanchez warned of a “long night ahead,” as the worst blackout to hit Europe in over a decade approached the 12-hour mark with no cause clearly identified and an uncertain timeline for the full restoration of power.

Befuddled passers-by holding torches and mobile phones squinted through pitch-black streets early on Tuesday and stranded travellers spent the night at train stations after a crippling backout plunged Spain into darkness.

The country’s top officials were trying to determine the cause of an outage that left tens of millions of people across the Iberian Peninsula without power.