By Ana Melgar, CNN en Español

(CNN) — After some areas of Puerto Rico welcomed the New Year in the dark amid a massive failure to the island’s power grid, service has been restored to nearly all impacted customers.

About 1.4 million users, or at least 98% of the total, had service Wednesday morning, according to LUMA Energy, the Canadian-American company responsible for power lines and transmission towers across the island.

The massive blackout, which began in the early hours of New Year’s Eve, highlighted the years-long issues with Puerto Rico’s crumbling power grid.

Gov. Pedro Pierluisi said Wednesday in a post on X he spoke with President Joe Biden and Secretary of Energy Jennifer Granholm, who reiterated the federal government’s “commitment to assist Puerto Rico in continuing and speeding up the reconstruction of the electric system.”

Puerto Rico governor-elect Jenniffer González-Colón, who is set to assume office Thursday, said she was in communication with her energy and security team to ensure power restoration is carried out in a coordinated, safe manner and with a sense of urgency.

While the cause of the blackout is still under investigation, the cause of the initial outage appeared to be an issue with an underground line, LUMA said.

The long-lasting structural issues with both generation and distribution were also linked to the massive blackout.

Josue Colon, the CEO of Puerto Rico Power Authority, said there was a breakdown in the transmission and distribution system that triggered a series of events that, in turn, caused all the generating units to stop operating.

The Puerto Rico Power Authority is a government-owned corporation that controls all the electricity generation, transmission and distribution properties on the island. The corporation has contracted LUMA since 2021 to manage the power grid, and Genera to lead energy production operations since 2023.

The New Year’s Eve outage is just the latest time that Puerto Rico’s power system has faltered on a mass scale. In 2017, Hurricane Maria left hundreds of thousands of people without power for months. Last year, about half of all electric customers on the island were at one point without power in the aftermath of Hurricane Ernesto, according to LUMA Energy.

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CNN’s Taylor Romine, Eric Levenson, Emma Tucker, Hanna Park, and CNN en Español’s Veronica Calderon contributed to this report.