Spain and Portugal have been paralyzed by a widespread power outage on Monday

A huge power outage struck Spain and Portugal around midday on Monday, paralyzing public transport and delaying flights, according to media reports. The cause of the blackout remains unknown.

The governments of the two EU nations have convened emergency cabinet meetings following the outage, which also briefly affected parts of France.

In Spain, blackouts were reported in Seville, Barcelona and Pamplona, with additional disruptions in Valencia. Metro services in Madrid and Barcelona were suspended, forcing passengers to evacuate trains and walk along the tracks, according to footage circulating online. Telephone lines were reportedly down across much of Spain, and Madrid's main airport was left without power.

Hundreds of people stood outside office buildings on Madrid's streets and there was a heavy police presence around key buildings, directing traffic and patrolling central atriums with lights, according to Reuters, citing witnesses.

A major tennis tournament in Madrid has been suspended due to the blackout. Spain's Channel 6 television has continued broadcasting in darkness.

Portugal and parts of southern France also reported network failures, according to local media.

Spain's national grid operator said a "major incident" in the energy transmission system may have caused the blackout. Power companies stated they were working to restore services as quickly as possible.

The president of Madrid's regional government, Isabel Diaz Ayuso asked Spanish Prime Minister Pedro Sanchez to authorize the use of the army if needed.

"We ask the national government to activate Plan 3 so that the Army can maintain order, if necessary," she said.

Sanchez is reportedly on an emergency trip to the headquarters of Red Electrica, the national grid operator, as officials are working "to understand the origin" of the outage and what can be done to resolve it quickly.

Speaking at a news conference, Red Electrica CEO Eduardo Prieto said the operation to restore power could take "between six and ten hours."

The Portuguese grid operator, Redes Energeticas Nacionais (REN), has said it is still too early to determine when power will be fully restored.

"At this time, it is still impossible to predict when the situation will be normalized," REN said in a statement, adding that it had "all resources deployed" to resolve the outage, according to AFP.

Senior European Commission Vice-President Teresa Ribera told Spanish Radio 5 that there was no evidence so far that the blackout was caused by a deliberate act such as sabotage or a cyberattack.