Spain and Portugal switched their power back on after the worst blackout in their history, though authorities offered little explanation for what had caused it or how they would prevent it from happening again.

Red Electrica, Spain's power operator, says that as of 06:00 local time (05:00 BST), 99.16% of power has been restored to mainland Spain. "All substations on the transmission grid are operational. We continue with the restoration work," the operator says.