Power had been restored to more than three-quarters of Puerto Ricans Thursday morning after a massive blackout knocked out electricity to the whole island Wednesday.

The Puerto Rico Electric Power Authority said 1.1 million out of its 1.47 million customers had power again as of 7 am Thursday:

AEE Informa: A las 7 am, ya más de 1,100,000 clientes tienen servicio eléctrico en toda la Isla. Seguimos... #hastallegar100 CC1 — AEE (@AEEONLINE) April 19, 2018

“We expect that our previously energized clients will have service in approximately 24 hours,” wrote PREPA deputy executive director Justo González Torres in a press release. “If a major complication arises, this period may be extended up to 36 hours.”

The outage is the second to affect the entire island in the six months since Hurricane Maria struck, and it once again undermined the fragile progress made in rebuilding the island after the destructive storm.

The Wednesday outage was caused by a bulldozer hitting a power line while trying to remove a collapsed transmission tower, according to El Nuevo Día. The line is a key choke point for Puerto Rico’s power grid, carrying electricity from generators in the south of the island to load centers in the north. The company responsible was D. Grimm, a subcontractor for Cobra Energy, which received a $200 million contract to repair Puerto Rico’s devastated power grid.

Cobra was selected alongside Whitefish Energy Services in the aftermath of the hurricane, but the deals drew scrutiny from Congress because the companies had limited experience in grid repair on such a large scale.

The blackout came less than a week after a tree fell on a crucial power line, knocking out power to 840,000 people. And there are still 61,000 utility customers who’ve been completely without power since September, the US Department of Energy reported earlier this month. Since “customer” typically refers to a household, which can encompass several people, estimates indicate that more than 100,000 people haven’t had power since the storm.

Since the storm hit, Puerto Rico’s 3.3 million residents have been forced to endure an agonizingly slow power restoration effort, suffering health and environmental harms as bureaucracy, logistical difficulties, and potential corruption hampered progress.

The ongoing blackout is the largest in US history and is now the second-largest in the world. Only Typhoon Haiyan, one of the largest tropical storms ever to make landfall and the deadliest storm ever to hit the Philippines, had a bigger impact on electricity service.

PREPA did manage to restore power to the Hiram Bithorn Stadium in San Juan Wednesday night in time for a Major League Baseball game between the Minnesota Twins and the Cleveland Indians.