It was not immediately known what caused the fire, although officials said the explosion knocked two other substations offline and caused a total loss of 400 megawatts worth of generation.
Thick black smoke billowed from the substation as neighbors in the area described on social media seeing the sky turn orange following a loud explosion.
NPR's Adrian Florido, reporting from San Juan, says the blackout affects the heavily populated northern part of the island after the explosion that occurred at about 9 p.m. Sunday.
RICARDO ARDUENGO via Getty Images An explosion at a power station plunged parts of northern Puerto Rico into darkness on Sunday evening.
Cruz famously clashed with President Trump past year over the federal government's response to the September 20, 2017 disaster. In late January, PREPA issued a statement saying more than 450,000 customers remained without electricity. Maria destroyed two-thirds of the island's power-distribution system and caused some $94 billion in damage.
The Category 4 storm cut power to much of the island.
Despite this, 65 people in shelters and an island-wide boil water advisory is still in effect even though nearly 100 percent of Puerto Ricans have access to drinking water, local government records show.
Aldi tops grocery store satisfaction survey
Among online supermarkets, Iceland claimed the top spot for the third year running but shared it with Ocado for the first time. But they were marked up for the quality of their fresh and own-label products.