San Juan, Puerto Rico - Power was restored to most of Puerto Rico Wednesday after a major blackout plunged the island into darkness on New Year's Eve.

Electricity supply had been restored to at least 1.44 million customers, or 98.3% of those affected, by noon 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.

The US took control of Puerto Rico, a Spanish-speaking archipelago, in 1898. The island's latest infrastructure issues, exacerbated by the devastating Hurricane Maria in 2017, come as many residents continue to seek greater control or independence.

China China launches 22-aircraft "combat patrol" into Taiwan

The utility company said power had been restored to both of the capital San Juan's major airports, key water supply facilities, and at least 31 hospitals.

Spokesperson Jose Perez warned, however, that power cuts could continue to affect some areas "as the power plants reach their optimum level."

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," he 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.

China China slams US with more sanctions over Taiwan military support

Those generators had been put in place following the impact of Hurricane Fiona in 2022.

Earlier, Luma's director of external affairs Perez told AFP 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 US mainland, and just hours ahead of New Year's Eve celebrations.