(CNN) An explosion and fire at a power substation caused a blackout in parts of northern Puerto Rico on Sunday, according to authorities.

Puerto Rico's Electric Power Authority (PREPA) said on Twitter that 400 megawatts of power generation had been lost.

The fire was caused by a mechanical failure and impacted sections of San Juan, Trujillo Alto, Guaynabo, Carolina, Caguas, and Juncos, PREPA spokesman Carlos Monroig told CNN.

Monroig said the majority of customers would have power restored Sunday night, but that communities powered by substations Villa Betina and Quebrada Negrito would likely be without power until Monday afternoon.

No injuries were reported, San Juan Mayor Carmen Yulin Cruz said.

No injuries were reported, San Juan Mayor Carmen Yulin Cruz tweeted on her verified account.

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