A fire at a Puerto Rico power plant triggered a widespread blackout. It's a worrying sign the island isn't ready for hurricane season.

Puerto Rico was hit by an island-wide power failure late Wednesday after a fire at a power plant. According to The Associated Press, more than 1 million people are without power on the island.

The exact cause of the fire remains unclear, according to Luma Energy, the Canadian-American private company that took over transmission and distribution of Puerto Rico's Electric Power Authority last year. The fire began at the power plant on the southwest coast of the island.

According to Luma Energy, power restoration efforts could last into Thursday and Friday. At least 118,000 customers had their power restored.

About 100,000 homes and businesses were affected by the power outage, according to Gov. Pedro Pierluisi. Nonessential government workers were told to stay home and the government canceled public school.

For some of the island's 3 million inhabitants, power interruptions could be life or death. They may use electricity to keep their medication cold. The generators at all hospitals and health centers were running and had enough fuel, according to the health secretary.

Kevin Acevedo, a vice president of Luma, told NBC News that the system is being restored little by little.

The island has an antiquated power grid and a warming world which causes more destructive storms. Warm air and sea surface temperatures can cause damaging wind speeds, large volumes of rain, and more intense storms.

Puerto Ricans pay more for power than Americans on the mainland, but the island's grid is unreliable and some customers were left without power for nearly a year after Hurricane Maria. The southern part of the island was hit by a series of earthquakes in 2020.

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While Puerto Rico's Electric Power Authority privatized transmission of the island's electricity last year, service is spotty and prices are high. Thousands of people took to the streets last year to protest the takeover.

The Puerto Rico Electric Power Authority did not reply immediately.

$12 billion in federal aid has been committed to modernizing Puerto Rico's electric grid, making it more resilient in the face of natural disasters. Hurricane season started in less than two months, but little work has begun on that end.