A massive power cut hit large parts of Spain and Portugal on Monday, causing widespread chaos and disruption.

The outage left millions of people without electricity, while internet and phone networks were also down.

Trains were cancelled and evacuated in some regions, traffic lights stopped working amid mounting delays at airports.

With shops, homes and restaurants plunged into darkness – and some people stuck in lifts – Spain’s electricity network said by mid-afternoon that restoring power could take several hours.

The cause remained unclear but there was “no indication” of a cyber attack, Portugal’s Prime Minister Luis Montenegro said.

The outage began around midday (13:00 BST) on Monday and its impact quickly escalated.

As the scale of the disruption became clear, residents of Madrid were warned to stay put, keep off the roads and not to call emergency services unless “truly urgent”.

A Spanish operator said power restoration would take up to 10 hours, while Portugal’s power firm REN said getting back to full power could take up to a week.

Queues formed at cash machines as card payments were affected by the outage, and there were reports that some petrol stations are closed.

Spanish media reported that some hospitals had implemented emergency plans, including halting routine work, news agencies reported.

By early evening and after several hours of blackouts, residents in some parts of the country reported the lights are back on.

Power was being restored “in several areas of the north, south and west of the [Iberian] peninsula”, the Spanish grid operator said.

The authorities in Spain and Portugal are still trying to work out what caused the power cuts.

“There are no indications of any cyberattack” at this point, the President of the European Council, Antonio Costa, said.

As panic spread earlier in the day, residents of Madrid were warned people to stay off the roads.

In a video on social media, the mayor of the Spanish capital, José Luis Martínez-Almeida, told residents to “keep their movements to an absolute minimum and, if at all possible, to remain where they are. We want to keep all roads clear.”

People should only call emergency services if it is “truly urgent”, he said.

“If emergency calls go unanswered, go to the police and the fire stations in person, where they will try to deal with all the emergencies.”

The country’s nuclear power plants automatically stopped when the blackout hit, and the Spanish oil company Moeve said it halted operations at its oil refineries.

Flights were also impacted, with delays and cancellations at some airports. EasyJet said it was experiencing some disruption to operations at Lisbon and Madrid. It said the situation was “fluid” and told customers to check local advice.

Businesses have been severely affected. Some Ikea branches in Spain switched to backup generators and stopped customers from entering its stores.

The Madrid Open Tennis organisers have decided to cancel Monday’s event.

Elsewhere, Andorra and parts of France were also hit, but the Balearic and Canary Islands were not affected.