US President Joe Biden says the full force of the federal government is ready to help Puerto Rico recover from the devastation of Hurricane Fiona.

Speaking at a briefing with Federal Emergency Management Agency (FEMA) officials in New York, Mr Biden said: “We’re all in this together.”

Mr Biden noted that hundreds of FEMA and other federal officials are already on the ground in Puerto Rico, where Fiona caused an island-wide blackout.

More than 60% of power customers remained without energy on Thursday, and a third of customers were without water — and local officials admitted they could not say when service would be fully restored.

Mr Biden said his message to the people of Puerto Rico who are still hurting from Hurricane Maria five years ago is: “We’re with you. We’re not going to walk away.”

That seemed to draw a contrast with former president Donald Trump, who was widely accused of an inadequate response to Maria, which left some Puerto Ricans without power for 11 months.

The hurricane was expected to still be at Category 4 force overnight when it passed close to Bermuda, where authorities opened shelters and announced schools and offices would be closed on Friday.

Fiona’s outer bands were already reaching the British territory on Thursday afternoon.

It was expected to still be a large and dangerously potent storm when it reached Canada’s Atlantic provinces, likely late on Friday, as a post-tropical cyclone.

“It’s going to be a storm that everyone remembers when it is all said and done,” said Bob Robichaud, warning preparedness meteorologist for the Canadian Hurricane Centre.

Hundreds of people in Puerto Rico remained cut off by road four days after the hurricane ripped into the US territory, and frustration was mounting for people like Nancy Galarza, who tried to signal for help from work crews she spotted in the distance.

“Everyone goes over there,” she said pointing toward crews at the bottom of the mountain who were helping others also cut off by the storm.

Dominican Republic Tropical Weather
Neighbours work to recover their belongings after the flooding caused by Hurricane Fiona in the Los Sotos neighbourhood of Higuey, Dominican Republic (Ricardo Hernandez/AP)

“No one comes here to see us. I am worried for all the elderly people in this community.”

At least five landslides cover the narrow road to her community in the steep mountains around the northern town of Caguas. The only way to reach the settlement is to climb over thick mounds of mud, rock and debris left by Fiona, whose floodwaters shook the the foundations of nearby homes with earthquake-like force.

At least one elderly woman who relies on oxygen was evacuated on Thursday by city officials who were working under a pelting rain to clear paths to the San Salvador community.

At least eight of 11 communities in Caguas are completely isolated, said Luis Gonzalez, municipal inspector of recovery and reconstruction.

It is one of at least six municipalities where crews have yet to reach some areas. People there often depend on help from neighbours, as they did following Hurricane Maria, a Category 4 storm in 2017 that killed nearly 3,000 people.

Puerto Rico’s government said some 62% of 1.47 million customers remained without power on Thursday. A third of customers, or more than 400,000, did not yet have water service.

“Too many homes and businesses are still without power,” Mr Biden said in New York, adding that additional utility crews were set to travel to the island to help restore power in the coming days.

The executive director of Puerto Rico’s Electric Energy Authority, Josue Colon, told a news conference that areas less affected by Fiona should have electricity by Friday morning.

But officials declined to say when power would be restored to the hardest-hit places and said they were working first to get energy to hospitals and other key infrastructure.

Neither local nor federal government officials had provided an overall estimate of damage from the storm, which dropped up to 30 inches of rain in some areas.

Fiona so far has been blamed for at least five deaths — two in Puerto Rico, two in the Dominican Republic and one in the French overseas department of Guadeloupe.

Fiona also hit the Turks and Caicos Islands on Tuesday, but officials there reported relatively light damage and no deaths.