Power in Spain and Portugal was gradually being restored late on Monday after a widespread outage that Portuguese energy company REN attributed to a rare atmospheric phenomenon caused by extreme temperature variations.

Authorities had initially said a cyberattack could not be ruled out, but the European Council said later in the day that there were no indications malicious cyber activity had been involved.

Jake Moore, global cybersecurity advisor at ESET, said the widespread power failure brought to life long-standing concerns over the disruption that could be caused by an attack on critical national infrastructure systems.

Traffic jams

The rare outage saw traffic paralysed as traffic signals failed, flights grounded, people trapped in lifts and energy cut to millions of homes and businesses.

The two countries’ governments convened emergency cabinet meetings while hospitals in Madrid and Cataluna in Spain suspended routine medical work, while continuing to attend to critical patients using backup generators.

In Spain retail businesses and several oil refineries were shut and reports said ATMs had gone dark.

In Madrid, Cader Ser Radio reported that parts of the Madrid metro system were being evacuated, with people trapped in stalled metro cars and elevators, and traffic jams occurring in the Madrid city centre after traffic lights failed.

Portuguese police said traffic lights had been affected across the country, while the metro system was closed in Lisbon and Porto.

Metropolitano de Lisboa, Lisbon’s metro transport operator, said some people had initially been trapped inside stalled trains.

Gradual restoration

Rede Electrica Nacional (REN) said it was “impossible” to predict when power could be restored in Portugal and that full restoration could take up to a week.

Spain’s grid operator Red Electrica said earlier in the day that restoration could take six to 10 hours, with power already restored in some areas in the west, south and north.

Parts of southern France were also affected by the outage for a short time. French grid operator RTE said it was providing supplemental power to parts of northern Spain after the outage began.

Ikea’s larger stores in Spain switched to backup generators but stopped new customers from entering the premises, with smaller city stores and pick-up points in Spain temporarily closed, the company said.

“We are letting our customers and co-workers stay in our stores in case they have no transportation options,” Ikea said in a statement.

In Portugal Ikea stores closed and would not reopen on Monday.

Airports continue to operate

Spanish intercity trains would not re-enter operations on Monday, with the goal being to resume services on Tuesday after control systems and safety mechanisms were restored, Spanish transport minister Oscar Puente said.

“Tonight we will prioritise repositioning trains and resetting systems over the maintenance work being carried out at night,” Puente said.

He said Spain’s airports were largely operating as normal using backup generators, with a 20 percent reduction in service for safety reasons.

Authorities had initially said they were investigating whether the outage could be due to a cyber-attack.

ESET’s Moore noted that such attacks by nation-states are “notoriously difficult to defend against” and targeting critical infrastructure has always been one of the biggest potential threats to a country.

“The increasing reliance on private companies to deliver public services unfortunately creates even more potential entry points for threat actors in the way of supply chain attacks too,” Moore said.