More than 1.3 million people living in Puerto Rico sat in darkness Tuesday morning after a sweeping blackout washed over the island.

As the country awoke to celebrate New Year’s Eve, a blackout hit, leaving people without electrical appliances, air conditioning, lights and more.

Luma Energy, the private company that oversees electricity transmission and distribution, said on X that the cause of the outage is under investigation but preliminary findings suggest a fault on an underground line. Restoring power could take anywhere from 24 to 48 hours.