Hurricane Fiona has struck the Turks and Caicos as a powerful Category 3 storm, threatening to devastate the tiny Caribbean archipelago after cutting a path of destruction through the Dominican Republic and Puerto Rico.
United States officials said the storm claimed four lives in Puerto Rico. A fifth person was killed in Guadeloupe earlier in the week.
US Health Secretary Xavier Becerra declared a public health emergency for Puerto Rico on Tuesday, 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 islands hours later.
Fiona is heading north towards Bermuda, with strengthening wind speeds of up to 201km/h, and is forecast to grow into a Category 4 in the coming days, the National Hurricane Center said.
The hurricane is on track to hit the eastern Bahamas on Wednesday.
On the Turks and Caicos Islands, a British Overseas Territory with 40 low-lying coral islands and a population of about 40,000, the government's National Emergency Operations Centre told residents of three eastern islands to shelter in place 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.
Officials warned powerful post-tropical conditions could hit Canada's Atlantic coast on Saturday.
The Dominican Republic and Puerto Rico, stunned by the storm's intensity, are struggling to cope with the aftermath.
US officials arrived in Puerto Rico - a US territory - on Tuesday to assess the damage.
Turks and Caicos Deputy Governor Anya Williams said power outages had hit five islands but no deaths had 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 US Coast Guard, with the British Navy patrol vessel HMS Medway helping with rescue efforts.