The death toll from Hurricane Irma is climbing with authorities reporting six patients at a Florida nursing home died after it had lost power, as millions struggle with no electricity and scarce essential services in the storm-hit state.
Irma, categorised as one of the most powerful Atlantic storms on record when it rampaged through the Caribbean, has killed at least 77 people, including 36 in the United States, officials said.
Some 4.3 million homes and businesses, or about 9 million people, were without power at midday Wednesday in Florida and nearby states.
The Florida Keys were particularly hard hit, with federal officials saying that 25 per cent of homes were destroyed and 65 per cent suffered major damage when Irma barrelled ashore on Sunday as a Category 4 hurricane with sustained winds of up to 215 km/h.
Another seven people died in Monroe County, which includes the Keys, officials said on Wednesday.
Police opened a criminal investigation at the Rehabilitation Center of Hollywood Hills, where two elderly residents were found dead at the facility and four later died at a nearby hospital, officials said.
More than 100 patients at the nursing home were evacuated on Wednesday along with 18 patients from a nearby facility that was cleared due to the criminal investigation, Hollywood officials said.
The centre had been without air conditioning, Broward County Mayor Barbara Sharief told reporters on Wednesday.
Prolonged power outages remains a risk for the elderly through the region, Sharief said.
Irma caused about $US25 billion ($A31 billion) in insured losses, including $US18 billion in the United States and $US7 billion in the Caribbean, catastrophe modeler Karen Clark & Co estimated on Wednesday.
Irma wreaked total devastation in parts of the Caribbean, where at least 43 people have died.