Power was restored to most of Puerto Rico on Wednesday after a major blackout plunged the island into darkness on New Year's Eve, the U.S. territory's electric utility said.
Electricity supply had been restored to at least 1.25 million customers, about 85.6% of those affected, by 10 a.m. local time, according to Luma Energy.
The power company said preliminary findings indicated a fault in an underground cable may have been the cause of the outage, although investigations continue.
Puerto Rico, a Spanish-speaking archipelago, came under U.S. control in 1898 and has faced perennial infrastructure issues, exacerbated by devastating hurricanes and a 2020 earthquake.
The utility company said power had been restored to both of the capital San Juan's major airports, key water supply facilities and to at least 31 hospitals.
Governor Pedro Pierluisi said he had spoken with President Joe Biden, and had asked for continuing Federal Emergency Management Agency (FEMA) support.
"This is a long and arduous process that requires local and federal collaboration, which is why I requested that FEMA continue facilitating the projects we have begun," Pierluisi said in a social media post.
He said Washington had approved a two-year extension for the use of temporary generators that provide the island 350 MW in energy, which will now continue to do so until 2027.
Those generators had been put in place following the impact of Hurricane Fiona in 2022.
Earlier, Jose Perez, Luma's director of external affairs, said the fault that initiated the power failure had caused a cascade effect that then led to the general blackout.
On Tuesday, Luma said it could take up to 48 hours for full restoration of power to all customers.
The blackout came as the Caribbean island entered its high season for tourists visiting from the wintry U.S. mainland, and just hours before New Year's Eve celebrations.