Puerto Rico repairs and investigates massive blackout 4:31
(CNN) --
Hundreds of thousands of homes and businesses in Puerto Rico remain without power Saturday, more than two days after the start of an island-wide blackout that began with a fire at a power plant.
Power has been restored to more than 1.3 million of the island's roughly 1.5 million utility customers, the territory's grid operator said early Saturday.
A blackout in Puerto Rico leaves several municipalities on the island without electricity
That leaves nearly 500,000 homes and businesses without power in a blackout that closed schools for two days and caused other disruptions for Puerto Rico's 3.2 million residents.
Power grid operator LUMA Energy was unable to commit to a timeline for power restoration for each customer, according to an announcement on its website.
"We are continuing to make progress on the restoration, but due to extensive damage to the Costa Sur Substation, we are not in a position to provide a full restoration estimate at this time," the power provider said.
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An unspecified fault sparked a fire at the plant outside the southwestern coastal town of Guayanilla around 8:45 p.m. Wednesday, knocking out power in Puerto Rico, said Kevin Acevedo, vice president of LUMA Energy.
Firefighters have since extinguished the flames.
All customers were without power initially, Josué Colón, Puerto Rico's principal telecommunications and infrastructure engineer, told reporters Thursday, "because all the generating units were disconnected."
The exact cause was not immediately known, the utility company said.
"Each piece of equipment (in the plant's switchyard) needs to be inspected and tested to ensure that when it's back in service, we can reliably and safely restore power for customers," said Shay Bahramirad, Vice President engineering and asset management senior at LUMA Energy, to reporters in San Juan on Friday.
The power outage has also disrupted water service to tens of thousands of homes and businesses, Gov. Pedro Pierluisi said, citing the island's aqueduct and sewer authority.
Puerto Rico canceled classes on Friday for students for the second day in a row.
But school principals, custodians and school cafeteria employees were still told to report to work on Friday, the island's education department said.
The island's courts were also closed due to the blackout, although some court services will be available online for urgent matters such as mental health and restraining orders, the territory's court system said.
All hospitals were operational Thursday afternoon, whether power was restored or they were operating through a generator, according to Interior Secretary Noelia García Bardales.
Power plant replacement parts ordered, official says
Early Thursday morning, the utility said the "massive island-wide blackout" could have been "caused by a circuit breaker failure" at the Costa Sur plant.
A firefighter battles flames at the Costa Sur power plant on Wednesday.
Firefighters extinguished the flames that affected two substations of the plant, the Puerto Rico Fire Department reported Wednesday.
The cause of the fire is being investigated, Acevedo said Thursday morning, adding that the crew was up to date with maintenance inspections.
Cleanup of the plant is already underway and spare parts have been identified and ordered, Acevedo said.
LUMA is a joint venture between Quanta Services and the Canadian energy company ATCO, which the government of Puerto Rico chose to take over the operation of the electric grid from its former electric utility, the Puerto Rico Electric Power Authority. Rich.
LUMA has been in charge of the power grid since June 1.
CNN's Rafy Rivera, Stefano Pozzebon, Michelle Watson, Rebekah Riess and Omar Fajardo contributed to this report.
Puerto Rico