At least six municipalities across island have areas cut off by storm which struck as a category 1 hurricane and has since strengthened

Bermuda and the Atlantic provinces of Canada were preparing for a blast from Hurricane Fiona as authorities struggled on Thursday to open roads for people left stranded and without power by the storm in Puerto Rico.

The storm was expected to still be at category 4 force when it passes close to Bermuda overnight and still dangerously potent when it reaches Canada, probably late on Friday, as an extratropical cyclone.

“It’s going to be a very large storm when it does make landfall,” said Bob Robichaud, warning preparedness meteorologist for the Canadian Hurricane Centre. “This is going to cover a fairly large area.”

Canadian officials were preparing for the possibility of flooding, washouts, storm surges and power outages.

Officials in Puerto Rico were working with religious groups, non-profits and others braving landslides, thick mud and broken asphalt to bring food, water and medicine to people in need. They were under pressure to clear paths so vehicles can enter isolated areas soon.

Nino Correa, commissioner for Puerto Rico’s emergency management agency, estimated that at least six municipalities had areas cut off by Fiona, which struck as a category 1 hurricane.

Manuel Veguilla said he had been unable to leave his neighborhood in the north mountain town of Caguas since Sunday.

“We are all isolated,” he said, adding that he worried about elderly neighbors, including his older brother who does not have the strength for the long walk to the closest community.

Veguilla heard municipal officials might open a pathway on Thursday but doubted that would happen because large rocks covered a nearby bridge and the 10ft space beneath it.

Neighbors have shared food and water dropped off by non-profit groups, and the son of an elderly woman was able to bring back supplies by foot on Wednesday, he said.

Veguilla said that after Hurricane Maria, a category 4 storm that struck five years ago and resulted in nearly 3,000 deaths, he and others used picks and shovels to clear the debris. But Fiona was different, unleashing huge landslides.

“I cannot throw those rocks over my shoulder,” he said.

Like hundreds of thousands of other Puerto Ricans, Veguilla had no water or electricity service. He said there was a natural water source nearby.

Fiona sparked an islandwide blackout when it hit Puerto Rico’s south-west and some 62% of 1.47 million customers remained without power on Thursday, four days after the storm, amid an extreme heat alert issued by the US National Weather Service. A third of customers, or more than 400,000, did not yet have water service.

The executive director of Puerto Rico’s electric energy authority, Josué Colón, told a news conference areas less affected by Fiona should have power by Friday. But officials declined to say when power would be restored to the hardest-hit areas.

“We are working by steps. Our next step is now to focus on” service to hospitals and other key infrastructure, said Daniel Hernández, the director of renewable energy for Luma Energy, which distributes power in Puerto Rico.

The US Federal Emergency Management Agency sent hundreds of personnel as the federal government approved a major disaster declaration and announced a public health emergency on the island.

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

The US National Hurricane Center said Fiona had maximum sustained winds of 130mph on Thursday morning. It was centered about 410 miles south-west of Bermuda, heading north-north-east at 15mph.

The Bermuda premier, David Burt, urged residents to “take care of yourself and your family. Let’s all remember to check on as well as look out for your seniors, family and neighbors. Stay safe.”

The Canadian Hurricane Centre issued a hurricane watch for Nova Scotia from Hubbards to Brule, Prince Edward Island, Isle-de-la-Madeleine and the coast of Newfoundland from Parson’s Pond to Port-Aux-Basques.

Jason Mew, a director with the Nova Scotia emergency management office, encouraged residents to fill-up on fuel, trim weak tree limbs and check on neighbors.

Hurricanes in Canada are rare, in part because once the storms reach colder Canadian waters they lose their main source of energy.

The storm 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.