Charles Ventura

USA TODAY

The vast majority of Puerto Ricans were without power Thursday after an enormous fire at an electrical plant left most of the island's 3.5 million people without electricity.

As of Thursday morning, 131,000 customers had power restored in the wake of Wednesday's blaze. Power is slowing being restored across the island, and the entire system should be back to normal on Friday.

Rolling power outages are expected to continue even as repairs occur, FEMA said.

The outage occurred after two transmission lines, with power running up to 230,000 volts, failed, the Electric Power Authority said.

Power was shut off island-wide as a safety precaution, FEMA said. All of the island's schools were closed Thursday.

Officials expressed their concern about the system failure.

“This is a very serious event,” Puerto Rico Gov. Alejandro Garcia Padilla said of the outage. “The system is not designed to withstand a failure of this magnitude. I assume complete responsibility. Everyone knows that the company’s maintenance problems began decades ago.”

Businesses, universities and government offices shuttered early Wednesday, creating chaos on roads. A police officer directing traffic was hit and taken to the hospital. Firefighters extinguished the blaze at the southern power plant, though cause of the fire is still unknown.

Airports, police stations and water plants are expected to receive first priority as power is restored to the island.

Puerto Rico’s power company has undergone a drastic financial rehaul, mostly stemming from the $9 billion debt it hopes to restructure amid corruption allegations.

Puerto Ricans, who continue to struggle in the midst of the island’s economic hardship, were angered about the power outage and expressed concerns on social media.

Contributing: The Associated Press; Doyle Rice, USA TODAY