The entire system is down. That means more than 3 million American citizens on the US commonwealth will be without power for four to six months.
"I do not know of any US state going without power for that long after a disaster," says David Merrick, director of the emergency management and homeland security program at Florida State University.
What can be expected from the US?
How will President Donald Trump respond?
President Donald Trump has told reporters that he will visit Puerto Rico, but has not said when.
"Puerto Rico was absolutely obliterated," Trump said this week. "We'll work with the governor and the people of Puerto Rico."
A White House official said Trump wants to visit, but the island might not be ready.
"He is committed to going, but date is still unclear," the official said. "There are significant infrastructure concerns."
Trump also issued major disaster declarations for Puerto Rico and the U.S. Virgin Islands, making federal funding available for temporary housing and home repairs, low-cost loans to cover uninsured property losses and other programs.
What is FEMA doing?
On Friday, the US Department of Homeland Security's Federal Emergency Management Agency was to begin delivering much-needed generators, meals, water, cots, blankets and other crucial supplies to the island.
FEMA says the US Energy Department will work with other agencies in power restoration efforts on the island.
How will Congress respond?
House Speaker Paul Ryan joined a bipartisan delegation of lawmakers Thursday
to help remove debris at a Friendswood, Texas, home damaged by Hurricane Harvey and vowed that Congress will take up legislation next month to get help to those impacted by recent natural disasters.
Ryan said that there was no official request from the Trump administration for additional assistance, but added: "I anticipate there will be more than one piece of legislation moving through Congress, but right now it's the short-term emergency needs and we are waiting to hear from the administration because they are totaling up what's going on in Florida, in Texas."
"We'll see what's the story in Puerto Rico, then we will get a request from the administration and then we will act on that request," he added, saying he expected a vote sometime in October.
Earlier this month, Congress approved and Trump signed into law
a package of bills that would send $22 billion for FEMA's disaster relief fund in a deal that also lifted the debt ceiling and kept the federal government funded through September.
Ninety representatives and 17 senators, all Republicans, opposed the legislation, some citing the fact that the legislation was part of a deal struck by Democratic leaders Nancy Pelosi and Chuck Schumer. Republican leaders had sought a debt limit increase for as long as 18 months.
All told, the package includes about $22 billion for FEMA's disaster relief fund, $15.25 billion of which is new, emergency funds, while another $6.7 billion was already slated to be in the spending measure that funds the government.
Expert: Disaster response should not be political
"Puerto Rico is eligible for the same disaster relief as any other state or territory," Merrick said. "That covers response and initial recovery. Beyond that? I'm not sure they'll get the same attention. They certainly need it."
Merrick said the fact that disaster aid packages have become political sets a dangerous precedent.
"Disasters and natural hazards aren't political," he said. "They don't only target members of a single party. Our response to disasters should not be political, either."
The repair and replacement of power lines and stations across the commonwealth could cost billions. The impoverished Spanish-speaking island has no voting power in Congress.
"We have to make the case that hardening the infrastructure and improving it in Puerto Rico and other hurricane-prone states and territories is going to save money over time in FEMA recovery costs," said Rep. Darren Soto, a Florida Democrat whose district includes Orlando.
More than half a million Puerto Ricans live in central Florida, according to a report by the Center for Latin American, Caribbean and Latino Studies at The Graduate Center of the City University of New York. About 1 million Puerto Ricans live in Florida, according to 2014 census data.
What can the island do to help itself?
Not much. Puerto Rico is already in an 11-year economic recession.
FEMA, Congress and private insurance firms will take on the lion's share of the rebuilding cost. But the island's cash-starved local government will have to take on some costs, too.
Puerto Rico is already suffering through an epic economic crisis. There's no way it could foot the entire bill itself. In May, it filed for the largest municipal bankruptcy in US history.
The island's utility authority also filed for a form of bankruptcy last summer, and Rosselló told CNN that the power grid already was "a little bit old, mishandled and weak."
Rosselló said officials believe some power stations are not badly damaged, but the distribution system is ruined. If transmission lines are in better shape than thought, power outages might be fixed sooner, the governor said.
Ricardo Ramos, CEO of the Puerto Rico Electric Power Authority, told CNN hospitals and water systems will get priority power restoration.
Authority officials surveyed some of the damage to the system from a helicopter on Thursday, Ramos said.
"Damage is catastrophic," he said. "Transmission lines on the ground and conductors on the ground, and distribution poles broken in half. [It's] very, very disconcerting."
Puerto Ricans will need to make lifestyle changes, Ramos said.
"It's a good time for dads to buy a ball and a glove and change the way that you entertain your children -- the way you're going to go to school, the way that you're going to cook, with gas stoves rather than electric," he said.
Still, federal relief funding may not be sufficient to fix the long-standing problems with the island's power grid, Merrick said.
"They will get some funding for recovery, but it probably won't be enough," he said. "Officials in [Puerto Rico] need to ensure that what money they do get is spent in a way that rebuilds the infrastructure to be more resilient."
Who else will help? New York steps up
The more than 5 million Puerto Ricans living in the US mainland also will be expected to step up.
"We're already having thousands of folks relocate from Puerto Rico to Florida," Rep. Soto said.
"We expect that to uptick to tens of thousands as commercial flights start running again. So I've encouraged my fellow central Floridians, open up their homes to their old neighbors, to family members, cousins, aunts, uncles and grandparents... while the grid and so many of these things we take for granted in life are reconstructed."
On Friday, New York Gov. Andrew Cuomo -- whose state is home to more than 1 million Puerto Ricans -- flew to the island with a delegation of elected officials and disaster experts to deliver more than 34,000 bottles of water, 9,600 ready-to-eat meals, 3,000 canned goods, 500 flashlights, 1,400 cots, 1,400 blankets, 1,400 pillows and 10 10kw generators.
"We're bringing large-scale generators with us that can power necessary facilities -- hospitals and communication centers," he said.
"But we're also bringing an assessment team of engineers in the power-supply industry to do a reconnaissance of the condition of the power system and the fastest way to get the power system back up."
Rep. Nydia Velazquez, D-New York, is part of the delegation. Hurricane Maria made landfall in her hometown, Yabucoa, on Wednesday morning.
"To me, this is personal," she said. "I have not been able to talk to my family yet."
She added: "When we touch down, we're going to see another Puerto Rico. But I can say this, the Puerto Rican people are resilient. And the great message we are providing to them is that in the darkest moment, we are going to be there ... We will never forget and we should never forget -- these are American citizens."