Three people were found dead at the Rehabilitation Center at Hollywood Hills and another three were pronounced dead at the hospital according to Hollywood officials.
Police obtained a search warrant on Thursday in their criminal investigation into the deaths, while Florida's healthcare agency ordered the nursing home to be suspended from the state Medicaid program.
At least 32 deaths have been reported in Florida and seven more combined in Georgia and SC.
After losing its full air conditioning on Sunday, the facility placed eight portable air coolers throughout the building and fans in the halls, state officials said in an emergency order late on Wednesday.
After whipping by the disaster of storm-force tropical winds and Hurricane Irma, many locations in the South Florida including the nursing home have been residing there without a power supply.
Some 4.3 million homes and businesses were still without power on Wednesday in Florida and neighboring states.
The deaths are now under a criminal investigation with the police refusing to rule anything out.
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Hurricane Irma has slammed into southwest Florida, threatening to bring risky storm surges to coastal areas, already battered by the hurricane's powerful winds.
Outages had fatal consequences at the Rehabilitation Center at Hollywood Hill, a nursing home in Hollywood, Fla., north of Miami.
But it was not until multiple patients began experiencing health emergencies, which promoted the evacuation of the center, that the utility company arrived to make the fix, the nursing home said.
Florida Gov. Rick Scott (R) said he would "aggressively demand answers on how this tragic event took place".
After the deaths were reported and the investigations launched, the Agency for Health Care Administration issued a moratorium keeping the nursing home from admitting any patients for the time being.
Local law enforcement said the nursing home had been without air conditioning for days following the storm, which made landfall last weekend. The Florida Health Care Association, a nursing-home industry group, said Wednesday morning that about 150 of almost 700 nursing facilities in the state do not have electricity fully restored.
The nursing home released a statement saying it had a "prolonged power failure to the transformer which powered the facility's air conditioning system as a result of the hurricane", CNN reported.
The Naples Municipal Airport also reported a gust of 142 miles per hour, near reports of 135mph gust and sustained winds of 93mph - the most powerful recorded gusts on the mainland.
"This is an inexcusable tragedy that frail patients would die of heat exhaustion without it being recognized and taking them to the hospital next door", Florida Senator Bill Nelson, a Democrat, said in a statement Wednesday. Police are going to the 42 other assisted living facilities in the area to check on those other residents.