Hurricane Isaias lashed the Bahamas as it churned toward Florida, bringing new dangers to a US state suffering record deaths from an unrelenting coronavirus outbreak.

The category one storm, packing winds of 120km an hour, gained strength after sweeping over the Dominican Republic, where homes were destroyed in the area of Hato Mayor.

The storm whipped the southeastern Bahamas and Turks and Caicos island chains with strong winds, the Miami-based National Hurricane Centre said.

"Some strengthening is possible today, and Isaias is expected to remain a hurricane for the next few days," it said.

The eye of the storm was expected to pass over southeastern Bahamas today and reach the central Bahamas during the night.

On its current path, it should be in the northwestern Bahamas by tomorrow and near Florida on Sunday, the forecasters said.

Hurricane warnings were up across the low-lying Bahamas while parts of Florida's east coast - including Palm Beach, the location of President Donald Trump's Mar-a-Lago resort - were under a hurricane watch.

Florida governor Ron De Santis signed an emergency declaration for counties on the exposed Atlantic coast.

But a slight shift westward in the storm's trajectory raised hopes that Florida will be spared a direct hit.

Mr DeSantis said it was too early to open shelters, but urged residents to stock up on enough water, food and medicine to last a week.

Residents stock up on supplies in preparation for Hurricane Isaias in Miami, Florida

Bahamas Prime Minister Hubert Minnis yesterday relaxed strict stay-at-home orders imposed because of the coronavirus to allow residents to prepare for the hurricane.

"I beg you, do not use this period for hurricane preparation to go socialising and visiting friends or family," he told a news conference.

"If you do not need to be out, please, please, stay at home! We are in the midst of a pandemic and if we do not act responsibly, the consequences could be dire," he said.

Isaias has already devastated Puerto Rico, downing trees and electric lines and inundating houses as it cut a path through the island yesterday.

View of a flooded street, after the passage of Isaias, in San Juan, Puerto Rico

"If you are seeing this, please, we need help," a man in Mayaguez, on the island's western side, begged in a video that showed his family clinging to the roof of their car as rising waters inundated their house.

In Florida, the concern was that if Isaias does hit, it would cause havoc at a time when hospitals are flooded with a surge of Covid -19 cases.

Florida today reported another 257 deaths, setting a fourth consecutive single day state record and pushing its virus death toll to 6,843. For several weeks, the state has had nearly 10,000 new coronavirus cases a day.