Tens of thousands of Puerto Ricans stunned by a hurricane that crushed concrete balconies, twisted metal gates and paralyzed the island with landslides, flooding and downed trees vowed to slowly rebuild amid an economic crisis as rescue crews fanned out across the U.S. territory Thursday.

The extent of the damage is unknown given that dozens of municipalities remained isolated and without communication after Maria hit the island Wednesday morning as a Category 4 storm with 249 km/h winds, the strongest hurricane to hit Puerto Rico in over 80 years.

Uprooted trees and widespread flooding blocked many highways and streets across the island, creating a maze that forced drivers to go against traffic and past police cars that used loudspeakers to warn people they must respect a 6 p.m. to 6 a.m. curfew imposed by the governor to ensure everyone's safety.

"This is going to be a historic event for Puerto Rico," said Abner Gomez, the island's emergency management director.

3rd-strongest storm

Previously a Category 5 with 281 km/h winds, Maria hit Puerto Rico as the third-strongest storm to make landfall in the U.S., based on its central pressure. It was even stronger than Hurricane Irma when that storm roared into the Florida Keys earlier this month.

In the capital of San Juan, towering eucalyptus trees fell nearly every other block over a main road dotted with popular bars, restaurants, and coffee shops, some of which were damaged. Outside a nearby apartment building, 40-year-old tourism company operator Adrian Pacheco recounted how he spent eight hours in a stairwell huddled with 100 other residents when the hurricane ripped the storm shutters off his building and decimated three balconies.

Hurricane Maria blasts through Puerto Rico1:21

"I think people didn't expect the storm to reach the point that it did," he said. "Since Irma never really happened, they thought Maria would be the same."

Hurricane Irma sideswiped Puerto Rico on Sept. 6, leaving more than a million people without power but causing no deaths or widespread damage like it did on nearby islands. Maria, however, blew out windows at some hospitals and police stations, turned some streets into roaring rivers and destroyed hundreds of homes across Puerto Rico, including 80 per cent of houses in a small fishing community near the San Juan Bay, which unleashed a storm surge of more than 1.2 metres

'I get goosebumps'

"Months and months and months and months are going to pass before we can recover from this," Felix Delgado, mayor of the northern coastal city of Catano, told The Associated Press.

The sound of chainsaws began to fill the silence that spread across San Juan late Wednesday afternoon as firefighters began to remove trees and used small bulldozers to lift toppled concrete light posts. Some neighbours pitched in to help clear the smaller branches, including Shawn Zimmerman, a 27-year-old student from Lewistown, Penn., who moved to Puerto Rico nearly two years ago.

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Rescue workers help a woman get to the Emergency Operation Centre after the area was hit by Hurricane Maria in Guayama, Puerto Rico. (Carlos Garcia Rawlins/Reuters)

"The storm didn't bother me," he said. "It's the devastation. I get goosebumps. It's going to take us a long time."

Maria has caused at least 10 deaths across the Caribbean, including seven in the hard-hit island of Dominica and two in the French Caribbean territory of Guadeloupe. Puerto Rico's governor told CNN one man died after being hit by flying debris. No further details were available, and officials could not be immediately reached for comment.

Island-wide power outage

Maria weakened to a Category 2 storm later in the day but re-strengthened to Category 3 status early Thursday with winds of 185 km/h. It was centred about 90 kilometres north of Punta Cana, Dominican Republic, and moving northwest near 15 km/h.

The hurricane was still dumping rain overnight Wednesday in Puerto Rico, where crumbled red roof tiles lay scattered across many roads, and curious residents sidestepped and ducked under dozens of black power lines still swaying in heavy winds. But they posed no danger: Maria caused an island-wide power outage, with officials unable to say when electricity would return.

Puerto Rico's electric grid was crumbling amid lack of maintenance and a dwindling staff even before the hurricanes knocked out power. Many now believe it will take weeks, if not months, to restore power.

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Residents of San Juan, Puerto Rico, deal with damage to their homes as Maria batters the island. (Hector Retamal/AFP/Getty Images)

Edwin Rosario, a 79-year-old retired government worker, said an economic crisis that has sparked an exodus of nearly half a million Puerto Ricans to the U.S. mainland will only make the island's recovery harder.

"Only us old people are left," he said as he scraped a street gutter in front of his house free of debris. "A lot of young people have already gone.... If we don't unite, we're not going to bounce back."

​33 requests for return to Canada

Global Affairs Canada says it is providing help to Canadians impacted by the storm and has received 33 requests for assistance to return to Canada.

It says Canadians in areas where there is an "avoid all travel" advisory are urged to leave on a commercial flight while they are still available.

And it says Canadians should contact their loved ones who may be in the path of the storm to ensure they are aware of the latest recommendations.

The Canadian Disaster Assistance Response Team has been deployed to the Caribbean region to evaluate urgent humanitarian needs, following a request from Dominica. Additionally, Global Affairs says the Canadian Armed Forces remain in the region and are prepared to help.

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A picture taken on Tuesday shows the powerful winds and rains of hurricane Maria battering the city of Petit-Bourg on the French overseas Caribbean island of Guadeloupe. (Cedrick Isham/AFP/Getty Images)

With files from The Canadian Press