Puerto Rico Gov. Ricardo Rosselló declared a state of emergency and activated the National Guard in preparation.
Those living on the commonwealth braced for the hurricane's potentially devastating winds and deluge, fearing if the Category 5 storm knocks out power from the bankrupt island's weakened electrical system, it may take weeks or months before power is restored.
Irma could be the strongest hurricane to ever hit the island, forecasters say. Some wonder whether Puerto Rico can rebuild.
"This is not a hurricane, this is a beast," a clerk in San Juan told CNN.
Another woman told CNN affiliate WAPA
the power "is something absolutely necessary, especially due to Puerto Rico's weather. We need to have the A/C or a fan on all night."
Last month, the director of Puerto Rico's power utility, Ricardo Ramos Rodríguez, said several factors have made the island's electric system "vulnerable and fragile," WAPA reported.
One of those is the shortage of employees. Many workers recently retired or left their jobs for better prospects on the US mainland, Ramos Rodríguez said.
Gov: Irma's magnitude 'never seen before'
Late Tuesday, Hurricane Irma was churning toward the northeastern Caribbean at 185 miles an hour. The forecast had it hitting around Antigua and Barbuda, St. Kitts and Nevis, and Anguilla by late Tuesday or early Wednesday, before impacting the British and US Virgin Islands and Puerto Rico later that afternoon.
The storm's path is uncertain but Florida was also bracing for Irma's impact, possibly this weekend.
"The magnitude of this storm ... has never been seen before in Puerto Rico," Rosselló said, WAPA reported. "Although we hope that this hurricane will not greatly impact Puerto Rico, we are bracing for what could be a very catastrophic event."
Alejandro De La Campa, director, FEMA's Caribbean Area Division, said the strongest hurricane to hit the island was a 160 mph storm in 1928.
"We haven't faced a threat like this in many, many years," he said, WAPA reported.
In a letter to President Donald Trump, Rosselló asked for federal assistance before the storm hit. The governor also asked the President to declare a state of emergency.
Rosselló wrote "the required assistance is crucial to lessen its impact on the island."
Government officials have identified more than 450 shelters across the island for citizens in flood-prone areas, the governor wrote.
'We're used to earthquakes'
In San Juan, people stood in long lines Tuesday afternoon at a Sam's Club, stocking up on water and gas canisters.
Joanna Martinez, who was in one of lines, said she finally found a store that still had water after trying a few stores.
Martinez, who has an 11-year-old and a 14-year-old, said she was worried about Irma's impact.
On another line, Yolie and Ron Goodman also wondered what devastation the storm would bring.
"We've never been through anything like this. We're used to earthquakes," said Yolie Goodman, who moved from Hermosa Beach, California, to Playa de Naguabo with her husband, Ron.
The retirees already had shored up their home by putting up storm covers.
Public schools and officials at the University of Puerto Rico campuses have canceled classes, and many businesses are closed.
"Make a U-turn and die in the ocean, Irma. The Caribbean islands don't need more problems!" Twitter user mujertropical wrote about the storm.
Puerto Rico's financial crisis
Puerto Rico could see natural devastation as it struggles with its own economic disaster.
The country's economy has declined over the years because of government overspending, a heavy dependence on debt and a costly, inefficient energy system. In May, the financial crises led the commonwealth to file the largest municipal bankruptcy in US history.
The US territory has $74 million in debt and another $50 million in pension obligations on the books.
Rosselló said the commonwealth has money ready in case of an emergency, despite the economic conditions. There is $15 million for an emergency fund set aside in the island's budget, officials said.