Portuguese grid operator REN will allow utilities to resume imports of electricity from Spain, but the transmission capacity will be limited to around one-third of the levels seen before the huge power blackout in the two countries on April 28.

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.

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.