SAN JUAN: Hurricane Fiona slammed into the Turks and Caicos Islands as a powerful Category 3 storm on Tuesday, dumping heavy rains and triggering floods on the Caribbean archipelago after cutting a path of destruction through the Dominican Republic and Puerto Rico.

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

U.S. Health Secretary Xavier Becerra declared a public health emergency for Puerto Rico on Tuesday night, freeing up federal funds and equipment to assist the island.

The storm slammed Grand Turk, the Turks and Caicos's biggest island on Tuesday morning, before hitting its main cluster of islands several hours later.

Strengthening with wind speeds of 125 mph (201 kmh), Fiona was heading north towards Bermuda on Tuesday night and was expected to strike as a Category 4 storm on Thursday, the National Hurricane Center (NHC) said.

Canadian officials warned of powerful post-tropical conditions hitting Nova Scotia, Newfoundland, New Brunswick and Price Edward Island by Saturday.

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," Williams told Reuters. She said her government was communicating with the British Royal Navy and U.S. Coast Guard, with the British Navy patrol vessel HMS Medway expected to arrive on Tuesday night to help with rescue efforts.

Jaquan Harvey, 37, a businessman who lives on Grand Turk, said wind drove rain water through the seams of the windows and doors as his house shook.

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

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 U.S. territory - on Tuesday 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.

PAINFUL ANNIVERSARY

Hurricane Fiona was a painful reminder of Puerto Rico's vulnerability. Tuesday marked the five-year anniversary of Hurricane Maria, a Category 5 storm which killed about 3,000 people and destroyed its power grid.

Thousands of Puerto Ricans still live under tarpaulin roofs.

Fiona made landfall in Puerto Rico on Sunday afternoon, dumping up to 30 inches (76.2 cm) of rain in some areas and triggering catastrophic flooding.

Nearly 80% of Puerto Rico remained without power on Tuesday, 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 here in 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.

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

On the Turks and Caicos Islands, a British Overseas Territory with a population of about 40,000 about 700 miles (1,125 km) southeast of Florida, the government told residents to shelter in place until further notice, and ordered businesses to close.

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 on Wednesday.

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 NHC once they reach Category 3 status, which is wind speeds of between 111mph and 129mph (178kmh-208kmh). A Category 4 storm has "catastrophic" wind speeds of between 130mph and 156mph. The most powerful Category 5 hurricane has wind speeds exceeding 157mph.

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 of people.

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.

As of Monday night, the country's emergency center counted more than 1.1 million people without drinking water and more than 700,000 without electricity.