SAN JUAN, Puerto Rico (CBSNewYork/AP) — An island-wide blackout has hit Puerto Rico, which is struggling with an increasingly unstable power grid nearly seven months after Hurricane Maria hit the U.S. territory.

Electric Power Authority spokeswoman Yohari Molina tells The Associated Press that crews are investigating the cause. Officials said Wednesday it could take 24 to 36 hours to fully restore power.

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It’s the first time since Category 4 storm hit on Sept. 20 that Puerto Rico has experienced a full island-wide blackout.

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Some 40,000 power customers were still without normal electricity service as a result of the hurricane.

CBS News’ David Begnaud reported the power authority is working to restore power to hospitals, the airport, gas stations, banks, shops and residences, in that order of priority.

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)