The Spanish and Portuguese governments convened an emergency cabinet meeting, and the reasons for the power outage are not yet clear.
Spain, Portugal and parts of southwestern France were hit by widespread power outages, paralyzing public transport, causing huge traffic jams, delayed flights, and the remaining residents were unable to get cash from ATMs as utility operators scrambled to restore the grid.
The Spanish and Portuguese governments convened an emergency cabinet meeting after Monday's power outage, which also briefly affected part of France, which borders northeastern Spain.
The head of operations at Spanish grid operator REE Eduardo Prieto told the press conference that it could take six to 10 hours to restore power to the Spanish grid.
Officials said authorities were unable to explain the cause at least an hour after the cause of the failure, although the cyber attack might not be ruled out and an investigation was underway.
The Spanish government urges residents to stay and avoid traffic chaos. "The government is working to determine the origin of this incident and specifically to resolve it as soon as possible," Prime Minister Pedro Sanchez's office said.
The European Commission said it was the basic reason for the power outages “contacting” with local authorities. A spokesman for the EU executive branch said: "The Commission will continue to monitor the situation and ensure a smooth exchange of information between all parties involved."
According to Cardena Sell Radio, there was traffic jam in downtown Madrid as traffic lights stopped working, as well as people trapped in the stagnant subway cars and lifts in the Spanish capital.
The panicked residents tried in vain to get the signal while the phone line was cut. "No (phone) coverage, I can't call my family, my parents, nothing: I can't even go to work," Carlos Condori told AFP. "People were shocked because this never happened in Spain."
In Cibeles Square, one of the busiest access in the Spanish capital, the power outage of traffic lights released police, whistles and car horns, as police tried to control traffic accumulation.
Valencia, Spain, reported that Al Jazeera's steps Vaessen said the power outage seemed temporary and that "everyone is in normal business". "But after a while it turned out to be bigger. The ATM didn't work and the traffic lights didn't work."
The Madrid Open Tennis Championship was suspended, forcing No. 15 seed Grigor Dimitrov and his British rival Jacob Fearnley to get out of the darkness of the scoring board, and the elevated cameras lost their power.
Portuguese police said traffic lights were affected across the country, with subways closed in Lisbon and Porto and trains not running.
"All plans to restore energy supply in phases are coordinated with European energy producers and operators," said Portuguese utility Ren.
A spokesperson said: "REN is in permanent contact with the official entity, i.e. the National Civil Defense Agency. Meanwhile, the possible causes of the incident are being evaluated."
In a later statement, due to the extreme changes in temperature in that country, Ren attributed the interruption to a rare atmospheric phenomenon in Spain. It added that it could take a week to fully restore the country's power grid.
In France, grid operator RTE said the power outage was brief but power had been restored. It is investigating the reasons.
"Currently, the electrical incident is affecting Spain and Portugal, and the reasons are yet to be determined," RTE said. "In France, in the Basque Country, houses are powerless for a few minutes. All power has since been restored."
RTE said its team has mobilized to assist Spanish grid operators, and RTE has restored 700MW of Spanish consumption through France.