SAN JUAN, Puerto Rico (AP) — A blackout hit Puerto Rico's capital and surrounding areas Thursday after two of the U.S. territory's main power plants shut down, a failure that came amid warnings from officials that the power company is struggling to remain operational.

The capital of San Juan was left without power along with the neighboring municipalities of Caguas, Bayamon and Carolina, company spokeswoman Yohari Molina told The Associated Press. More than 970,000 people live in the areas hit by the blackout, though Molina said it wasn't clear how many were affected.

Officials for the Electric Power Authority announced in the afternoon that power had been restored to the island's main international airport and several hospitals. Several hours later, they said a break found in a main transmission line just miles from a power plant in the island's south had been repaired and electricity was slowly being restored.

The utility said the Palo Seco and San Juan plants shut down to protect the electrical system. A backup power line in the area of the failure has not been repaired since Hurricane Maria hit the island Sept. 20.

While officials said the outage was limited to four municipalities, people on social media reported outages in other areas as well. The blackout snarled traffic and knocked out water service to dozens of neighborhoods, including the historic part of Puerto Rico's capital known as Old San Juan.

The outage came nearly three weeks after a fire at a substation knocked two power plants out of service and left some people without power for two days. An investigation into that incident is still underway.

Juan Manuel Fernandez, a customer service representative who lives in Caguas, was affected by Thursday's blackout as well as the Feb. 11 outage, which occurred just days after crews restored power in his neighborhood more than five months after Hurricane Maria.

"You just resign yourself," he said of the newest outage. "It's become normal."

Overall, more than 15 percent of power customers remain in the dark nearly six months after the hurricane, which destroyed two-thirds of the island's power distribution system. Officials have said they expect power to be fully restored by May.

Meanwhile, a federal control board overseeing the island's finances recently obtained a $300 million loan for the power company, warning that would only serve to keep it operational through late March. Board members said they expect to request more loans in upcoming weeks.

Gov. Ricardo Rossello announced in January that he plans to privatize the power company in 18 months. The company is $9 billion in debt and operating with infrastructure that is nearly three times older than the industry average.

"This is another opportunity to reflect (on privatization)," he said shortly after the blackout. "We cannot rebuild the same system."