The hunt has begun for the cause of a massive blackout across Spain, Portugal and parts of France that halted trains, bank machines and traffic lights, in one of Europe's biggest ever power system collapses.

The sweeping power outage that hit Spain and Portugal this week has raised questions about the electricity grid in a region not normally known for blackouts.

Spain and Portugal experienced a widespread power outage on Monday, leaving millions without electricity in a snap blackout. In Portugal, official sources told domestic media that the outage, which hit around late morning local time,