SAN JUAN, Puerto Rico (AP) — A major power outage has hit Puerto Rico, plunging hundreds of thousands of customers into darkness after a fire erupted at one of the largest power plants in the U.S. territory.

Wednesday night’s outage is one of the biggest reported in recent months for the island’s crumbling electrical grid, which has seen its periodic blackouts grow worse the last few years.

Puerto Rico’s power authority shared video of the fire.

The private company that took over transmission and distribution of the Puerto Rico’s Electric Power Authority last year says power may not be restored until Thursday because of “the size and scope” of the outage.

Gov. Pedro Pierluisi tweeted that it would take an estimated 12-24 hours for power to return. He said priority would be given to hospitals and basic services. Pierluisi urged people to remain calm.

Officials tweeted several water facilities were out of operation, impacting drinking water. Service for around 100,000 customers was impacted, officials said. Workers were mobilized to restore service.