Puerto Rico woke up in darkness on Tuesday morning after a power grid failure left nearly all of the island without electricity.
Around 90 per cent of clients were without power at 9:30 a.m. (1730 GST), according to energy distribution company Luma Energy's real-time portal.
It will likely take 24 to 48 hours to turn the lights back on, "conditions permitting," Luma said in a statement.
"While the cause of the outage is under investigation, preliminary findings point to a failure in an underground line," Luma added.
Ivan Baez, a spokesperson for power generator Genera, called the grid failure a "major incident" in a local radio interview.
He said that the line believed to have failed was operated by Luma and brought down plants belonging to Genera as well as private generators.
Genera's website showed two plants starting up again at 9:30 a.m. in the U.S. territory.
Puerto Rico has long dealt with chronic power outages as its infrastructure crumbles. It was hit hard by Hurricane Maria, a Category 4 storm, in 2017.
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