By late Sunday, electricity workers had been able to restore power to key locations, including the Luis Muñoz Marín International Airport in Carolina, as well as the Medical Center.
A blackout hit northern Puerto Rico late Sunday after an explosion set off a major fire at a main power substation in the USA territory.
The hurricane tore through Puerto Rico with 155-mile-per-hour winds and pummeled the island with more than 30 inches of rain, leaving a deadly path of destruction in its wake.
"It appears fire has nearly totally been extinguished and the cooling phase is beginning".
Quinones says he can't say how many customers remain without power as a result of Sunday's outage, which affected the island's northern region.
No injuries were reported, San Juan Mayor Carmen Yulin Cruz tweeted on her verified account. The storm killed dozens and left the entire island without power at a time when it was already trudging through the largest government bankruptcy in the United States history, with some $120 billion in combined bond and pension debt.
In many cases, power workers are repairing equipment that should have always been replaced but remained online due to the power authority's long financial crisis.
Puerto Rico's governor announced last month that he plans to privatize the company, which relies on infrastructure almost three times older than the industry average.
"We are trying to restore that as quickly as possible", the company told The Associated Press.