An explosion at a power station in Puerto Rico left the northern part of the island and portions of San Juan without power Sunday night, according the island’s power authority.

The Puerto Rico Electric Power Authority said Sunday one of the island’s power stations suffered a breakdown and exploded, knocking out substations and leading to the loss of 400 megawatts worth of power generation.

AEE Informa: El interruptor 36210 de Monacillo sufrió una avería, explotó y causó la pérdida de unidades en la Central San Juan y Palo Seco, que afecta el servicio en varios municipios del área metro, así como del área de Caguas y Juncos. CC1 — AEE (@AEEONLINE) February 12, 2018

AEE Informa: Con el evento se perdieron 400 megavatios de generación y estamos comenzando a recuperarlos lo antes posible. CC1 — AEE (@AEEONLINE) February 12, 2018

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Power authority staff were working to restore the system as of Sunday night. The cause of the explosion was not immediately clear.

Puerto Rico Gov. Ricardo Rosselló said last month he plans to sell the assets of the island’s power system to the private sector in an effort to improve service.

Much of Puerto Rico is still recovering from the effects of Hurricane Maria, which devastated the island in late September.

The power authority reported earlier Sunday that roughly 75 percent of customers have had electricity restored since the storm, according to ABC News.

The official death count from the hurricane is 64 people, but multiple analyses have found the number is likely more than 1,000. A Puerto Rican journalists’ organization is suing over the low official death count.