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.

For millions of people across Spain and Portugal, power was lost in an instant yesterday. Communications came to a halt, water was not running in places, metro systems ground to a standstill, and travellers were strained in airport departure lounges.

Much of Spain’s power grid was operating normally on Tuesday, a day after a blackout affected critical infrastructure across the Iberian Peninsula.