Madrid [Spain], April 29 (ANI): A massive and unexplained 12-hour power outage has plunged Spain and Portugal into chaos, disrupting traffic, airports, and daily life, prompting both countries to declare a state of emergency, CNN reported.

Prime Minister Pedro Sanchez said that almost 50 per cent of Spain's electricity supply has been restored after Monday's massive power outage.

The cause of the outage is still unknown, but it's believed to have occurred when 15 gigawatts of power were lost suddenly, according to Sanchez.

'This is something that has never happened before,' he said. 'To give you an idea, 15 gigawatts is equivalent to approximately 60 per cent of the country's demand at that time.'

According to CNN, Spain will try to restore electricity nationwide by Tuesday morning, but the prime minister acknowledged that officials still can't say with certainty when things will return to normal.

'The situation is very asymmetrical across the country. Some autonomous communities have already recovered up to 97 per cent of their supply, while others, unfortunately, are below 15 per cent,' he said.

Spain's Interior Minister Fernando Grande-Marlask declared a state of emergency in several regions, including Andalusia, Extremadura, Murcia, La Rioja, and Madrid.

Meanwhile, Portugal's Prime Minister, Luis Montenegro, announced a crisis due to the energy emergency.

'We have learnt of a general blackout in the electricity grid, which originated outside our territory, most probably in Spain,' Prime Minister Luis Montenegro said in a televised address.

The Portuguese government has set up a crisis office to manage the 'unprecedented' situation and has urged citizens to reduce their energy consumption while authorities work to fully restore power, as per CNN.

Earlier, due to power outage, several passengers have been left stranded in the metros in the capitals of Spain and Portugal, with trains stuck in the tunnels between stations, Euronews Portugal reported.

The Spanish government gathered for an emergency session at Moncloa and is monitoring the situation, it reported. (ANI)