ISTANBUL

Portugal’s grid operator said Monday that fully restoring power could take up to a week following a blackout that has crippled the country.

“Due to the complexity of the phenomenon and the need to rebalance electricity flows internationally, it is estimated that full normalization of the network could take up to a week,” said Rene Electrica Nacional (REN), according to BBC News.

REN noted that the blackout was a result of a “fault in the Spanish electricity grid” which was related to a "rare atmospheric phenomenon.”

“Extreme temperature variations in Spain contributed to the outage,” said REN officials.

Portuguese Prime Minister Luis Montenegro also noted that the blackout did not initiate in Portugal, pointing to Spain.

“It will be a few hours, and we all need to be patient because objectively, the situation is very uncomfortable, but it is not a reason for alarm or for behaviors that are different from those of a normal day,” Montenegro said according to the Publico daily.

He said there is currently “no indication” of a cyberattack while noting that no scenario was “out of the question.”

Having spoken with Spanish Prime Minister Pedro Sanchez, European Council President Antonio Costa also said there were “no indications” of any cyberattack at this point.

"The causes are still being studied. It's better not to speculate," said Sanchez, according to El Pais.

Sanchez also announced that the government would assume the management of the blackout in Andalusia, Extremadura and Madrid following requests from those regions.

He further urged people to avoid travel and to use cell phones only for short calls.

Spanish energy provider Red Electrica noted that the outage is “exceptional and totally extraordinary” and would take six to 10 hours to repair.

“Voltage has already been restored at substations in several areas in the north, south and west of the mainland, beginning to supply electricity to consumers in those areas,” the Spanish energy company confirmed to Anadolu, adding they would gradually restore the electricity supply.

REN reaffirmed late Monday that it was difficult to predict when things would be completely back to normal, although it is expecting that everything will be normalized on Tuesday morning.

"We are still not entirely sure about the causes, but moments before, we saw a large voltage fluctuation in the Spanish network. Our system was importing, and as a result, the control systems went off and there was a total imbalance," said REN administrator Joao Faria Conceicao.

He assured that they would continue to restore power across Portugal as some districts had already started to receive power supply, according to the Diario de Noticias daily.

"The expectation is that power will be restored in Greater Porto within two hours. Greater Lisbon will take longer because there are fewer power plants nearby. Lisbon could be connected within five to six hours, at least in terms of priority consumption," Conceicao noted.

The electricity went out across Portugal, Spain and Andorra around midday Monday, also affecting parts of France as authorities are still investigating the causes of the outage.

*Beyza Binnur Donmez from Geneva contributed to this story