Several major cities in Europe were thrown into total darkness in the early hours of Monday after the power grid collapsed in Spain, France and Portugal, causing widespread blackouts.

According to Reuters, the blackouts caused major disruptions including flight cancellations, paralysed traffic and people left stranded inside elevators in several parts of the three countries as authorities scrambled to restore electricity to millions of homes and businesses.

The severity of the situation prompted the governments of Spain and France to convene emergency cabinet meetings, with officials initially panicking about a possible cyber attack as outages of such scale are extremely rare in Europe.

Hospitals in Spanish cities of Madrid and Catalonia were forced to resort to backup generators to continue attending to critical patients after they suspended all routine medical services.

The cause of the outages is still unclear but officials have ruled out cyber attack, with the President of the European Council Antonio Acosta saying there’s “no indication” of a cyber attack.

Meanwhile, witnesses told Reuters that power had started returning to Basque country and Barcelona areas of Spain a few hours after the blackouts in early afternoon. It is unclear whether power has been fully restored across the three countries.