Hurricane Fiona has hit the Turks and Caicos Islands as a powerful Category Three storm - slamming the Caribbean archipelago with heavy rains and life-threatening flooding after cutting a path of destruction through the Dominican Republic and Puerto Rico.

US officials said the storm had claimed four lives in Puerto Rico. A fifth person was killed in Guadeloupe earlier in the week.

This morning, the storm slammed Grand Turk, the Turks and Caicos's biggest island, and was moving closer to the main cluster of islands by afternoon, the US National Hurricane Center said in its 11am Eastern update.

Fiona was on track to head north toward the eastern seaboard of North America, with Canadian officials warning of powerful post-tropical conditions hitting Nova Scotia, Newfoundland, New Brunswick and Price Edward Island by Saturday.

In a telephone interview with Reuters, Turks and Caicos Deputy Governor Anya Williams said power outages had hit five islands but no deaths had yet been reported.

"Shutting the country down early is what helped us save lives," Ms Williams said.

She said her government was communicating with the British Royal Navy and US Coast Guard, with the British Navy patrol vessel HMS Medway expected to arrive tonight to help with rescue efforts.

The low-lying Turks and Caicos Islands are braced for Hurricane Fiona's arrival
The low-lying Turks and Caicos Islands

Jaquan Harvey, 37, a businessman who lives on Grand Turk, said that he and his neighbors learned some lessons from Hurricane Maria five years ago, a massive Category Five storm, and were well prepared with supplies of food and water, and securing their property.

Mr Harvey said during the worst of Fiona, wind drove rain water through the seams of the windows and doors as the whole house shook.

At about 8am this morning, the eye passed over Grand Turk.

"It was very loud, like there were giants outside shouting and roaring," Mr Harvey said. "You could feel the pressure of the air as everything rattled."

Puerto Rico

To the south, the Dominican Republic and Puerto Rico were stunned by the storm's intensity and were struggling to cope with the aftermath.

Deanne Criswell, head of the Federal Emergency Management Agency (FEMA), arrived in Puerto Rico - a US territory - today to assess the damage, agency officials said.

Officials said multiple FEMA teams, including two search and rescue units, were being deployed and several hundred FEMA personnel were already on the island.

Hurricane Fiona was a painful reminder of Puerto Rico's vulnerability.

Today marked the five-year anniversary of Hurricane Maria, which killed about 3,000 people and destroyed its power grid.

Thousands of Puerto Ricans still live under makeshift tarpaulin roofs.

Fiona made landfall in Puerto Rico on Sunday afternoon, dumping up to 30 inches of rain in some areas.

Nearly 80% of Puerto Rico remained without power today, according to Poweroutage.us.

Officials said it would take days to reconnect the whole island of 3.3 million people.

"It knocked down many trees, there are downed poles and herein the house we got water where it had never happened before," said Asbertly Vargas, a 40-year-old mechanic in Yauco, a town along the island's southern coast.

"A fence in the yard fell down and the land in the back slid a bit towards our house. But I'm fine, I'm alive."

A flooded street is seen after the passage of Hurricane Fiona in Salinas, Puerto Rico
A flooded street is seen after the passage of Hurricane Fiona in Salinas, Puerto Rico

Puerto Rico power provider LUMA Energy said it had restored electricity to 100,000 customers but that it would take days for full restoration.

Puerto Rico's grid has long been criticized as unreliable, but residents and consultants have complained that outages have become more frequent since LUMA took over operations last year.

The grid is largely owned by the Puerto Rico Electric Power Authority (PREPA).

On the Turks and Caicos Islands, a British Overseas Territory with 40 low-lying coral islands and a population of about 40,000 about 1126 km southeast of Florida, the government's National Emergency Operations Center (NEOC) told residents of three eastern islands to shelter in place, and ordered businesses to close.

Turks and Caicos Premier Washington Misick, who attended the funeral of Queen Elizabeth II, issued a statement from London warning residents to prepare for the storm.

Foreign governments issued travel alerts for the islands, a popular tourist destination.

Similar preparations were under way in the eastern Bahamas, which the storm could skirt tomorrow, when it was forecast to turn in a northwesterly track toward Bermuda.

It could mushroom into a Category 4 storm in coming days, reaching Canada's Atlantic coast by late Friday, the NHC said.

Hurricanes are deemed "major" by the National Hurricane Center once they reach Category Three status, which is wind speeds of between 178kmh-208kmh.

A Category Four storm has "catastrophic" wind speeds of between 209kmh-251kmh.

The most powerful Category Five hurricane has windspeeds exceeding 252kmh.

View of a park in Samana, Dominican Republic, after the passage of Hurricane Fiona today

Dominican Republic

In the Dominican Republic, severe flooding limited road access to villages, forced 12,500 people from their homes and knocked out power to hundreds of thousands.

Fiona was the first hurricane to score a direct hit on the Dominican Republic since Jeanne left severe damage in the east of the country in 2004.

Dominican Republic President Luis Abinader canceled plans to attend the United Nations General Assembly to address the emergency.

As of last night, the country's emergency centre counted more than 1.1 million people without drinking water as a result of failures in aqueducts and more than 700,000 without electricity, especially in the east of the country.

"It is my main duty to meet the needs and urgencies that are needed at this time in our country," Abinader said in a video posted last night on social networks.