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SAN JUAN, Puerto Rico — A blackout hit Puerto Rico's capital and surrounding areas on Thursday after two of the U.S. territory's main power plants shut down as officials warn the power company is struggling to remain operational.

The capital of San Juan was left without power, along with the neighboring municipalities of Caguas, Bayamon and Carolina, company spokeswoman Yohari Molina told The Associated Press. She said crews were working to repair the problem but that wasn't clear how many customers were affected by the outage. More than 970,000 people live in the areas hit by the blackout.

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Puerto Rico's Electric Power Authority tweeted that the Palo Seco and San Juan plants shut down to protect the electrical system, but it is unclear what caused the shutdown. Officials said they aimed to restore power by Thursday afternoon.

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The power outage comes nearly three weeks after a fire erupted at one of the company's substations, knocking two power plants offline, leaving some people without power for two days. The investigation into that incident is still ongoing.

Overall, more than 15 percent of power customers still remain in the dark nearly six months after Hurricane Maria, which destroyed two-thirds of the island's power distribution system. Officials have said they expect power to be fully restored by May.

Meanwhile, a federal control board overseeing the island's finances recently obtained a $300 million loan for the power company, warning it will only serve to keep it operational through late March. Board members said they expect to request more loans in upcoming weeks.

Gov. Ricardo Rossello announced in January that he plans to privatize the power company in 18 months. The company is $9 billion in debt and operating with infrastructure that is nearly three times older than the industry average.

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