Spanish power distributor Red Eléctrica said that restoring power to large parts of the country after a massive and unprecedented outage Monday that also hit Portugal could take six to 10 hours. 

The company declined to speculate on the causes of the blackout. The Portuguese National Cybersecurity Center issued a statement saying there was no sign the outage was due to a cyberattack. 

Eduardo Prieto, head of operations at Red Electrica, told journalists it was unprecedented, calling the event "exceptional and extraordinary." 

The outage hit across Spain and Portugal, including their capitals, knocking out subway networks, phone lines, traffic lights and ATM machines.

Play at the Madrid Open tennis tournament was suspended. The ATP men's tour said that two singles matches and one doubles match were in progress when power went out

Authorities said the cause was not immediately known.

The Portuguese cabinet convened an emergency meeting at the prime minister's residence, and Spanish Prime Minister Pedro Sanchez visited power distributor Red Electrica to follow efforts at restoring grid operations.

The countries have a combined population of over 50 million people. It was not immediately clear how many were affected.

It is rare to have such a widespread outage across the Iberian Peninsula. Red Electrica said the incident was being assessed.

A couple of hours later, Spain's electricity network operator said it was recovering power in the north and south of the peninsula, which would help to progressively restore the electricity supply nationwide.

Portuguese distributor E-Redes said the outage was due to "a problem with the European electricity system," according to Portuguese newspaper Expresso. The company said it was compelled to cut power in specific areas to stabilize the network, according to Expresso.

Spain's public broadcaster RTVE said a major power outage hit several regions of the country just after midday local time, leaving its newsroom, Spain's parliament in Madrid and subway stations across the country in the dark.

People rush to buy generators

A graph on Spain's electricity network website showing demand across the country indicated a steep drop around 12:15 p.m. local time from 27,500 megawatts to near 15,000 megawatts.

Video aired on Spanish television showed people evacuating metro stations in Madrid and empty stations with trains stopped in Barcelona.

Spain's traffic department is asking citizens to avoid using their cars as much as possible due to the power outage, which has affected traffic lights and electrical road signage.

In Terrassa, an industrial town 50 kilometres from Barcelona, stores selling generators were out of stock after people lined up to buy them.

Portugal's E-Redes said parts of France, which shares its southwest border with Spain, also were affected.

In Portugal, a country of some 10.6 million people, the outage hit the capital, Lisbon, and surrounding areas, as well as northern and southern parts of the country. Portuguese police placed more officers on duty to direct traffic and cope with increased requests for help, including from people trapped in elevators.

Portuguese hospitals and other emergency services switched to generators. Gas stations stopped working and trains stopped running.

Portugal's National Authority for Emergencies and Civil Protection said backup power systems were operating.

Several Lisbon subway cars were evacuated, reports said. Also in Portugal, courts stopped work and ATMs and electronic payment systems were affected. Traffic lights in Lisbon stopped working.

It was not possible to make calls on mobile phone networks, though some apps were working.