SAN JUAN, Puerto Rico — Electricity was restored to most of Puerto Rico by Saturday following a rare, islandwide blackout caused by a power plant fire, the territory’s power utility said.

Fewer than 20,000 clients remained without power in some parts of San Juan and other urban areas.

“We have been operating under normal conditions since 2:30 a.m.,” said Puerto Rico Electric Power Authority Executive Director Javier Quintana, noting that 60 hours had passed since power was knocked out for most of the island’s 1.5 million homes and businesses, affecting the majority of the island’s 3.5 million residents.

Officials said about 50,000 clients, mostly in the island’s northeast area, remained without water service, which was interrupted for some people because many filtration plants and pumping stations need electricity to run and don’t have generators for emergencies.

Authorities hoped to dramatically lower the number of people without water on Saturday.

The blackout occurred as Puerto Rico’s troubled power company seeks to restructure $9 billion in debt and find the money needed to update the island’s aging electrical grid.

In the wake of the outage, Puerto Rico’s Energy Commission said late Friday it was rejecting a 20-year development plan proposed by the utility and impose its own version, one it said would better deal with the grid’s infrastructure problems.

Utility officials did not immediately respond to requests for comment.

Such development plans are typically used by electricity companies to describe the steps they will take to operate and adhere to government regulations.

At least one person died from carbon monoxide after setting up a personal generator.