More than 800,000 Puerto Ricans are without power after a cyberattack and a large fire knocked out power across the island.
The fire occurred on Thursday at a facility operated by Luma Energy, a new energy provider on the island.
By midnight, 60,000 customers were still without power.
"The fire caused major blackouts across the entire island. The situation is under assessment and work is being done to restore the system," LUMA Energy said in a tweet.
Earlier on Thursday, the energy company announced that it had been targeted by a cyberattack that locked users out of access to the company's online services.
NPR reports that the cyberattack was a distributed denial of service attack, which locks up online services by bombarding them with connection requests. During the attack, two million visitors per second were logged, which locked many users out.
The company released a statement following the attack saying that it "regrets that its customers experienced the inconvenience the attack may have caused and looks forward to continuing to provide them with an exceptional customer service experience."
It was not immediately clear if the fire and the cyberattack are linked.
Officials asked residents for patience while Luma - which has only been in operation on the island for 10 days - took over control of the islands' power systems.
The rollout of the new company has been difficult; even before the fire, more than a million customers had experienced power outages since the beginning of June.
The Governor of Puerto Rico, Pedro Pierluisi, said that both state and federal law enforcement authorities were investigating what he called an "explosion."
"Whoever is responsible for it will have to answer to the People of Puerto Rico," Mr Pierluisi said.
FBI officials in San Juan said they were "evaluating" the outage and attack, and have asked that anyone with information come forward.
The blackout hit the island at a time when healthcare authorities are working to vaccinate the population. Several coronavirus vaccines require low temperatures for storage, meaning a blackout could potentially cause doses to expire due to a lack of refrigeration.
Health Secretary Carlos Mellado Lopez tweeted that the island's hospital services were not interrupted by the fire or the attack and that their stock of vaccines had not expired.
"Our suppliers have generators and we have over 70 support centres to keep them safe," he wrote.