Nursing home officials blamed a blown transformer for cutting power to the air conditioning unit.
"We're conducting a criminal investigation inside", Hollywood Police Chief Tom Sanchez said.
One resident already was dead when police got a call at 4 a.m.
Numerous patients were placed on stretchers and taken to Memorial Regional Hospital. And at the huge, 15,000-resident Century Village retirement community in Pembroke Pines, where there were also widespread outages, rescue workers went door to door in the 94-degree heat checking on residents and bringing ice, water and meals. The only major difference, for instance, between his comments Wednesday evening to reporters and his statements before his 2014 reelection is that he no longer says, "I'm not a scientist".
Miami-Dade County Mayor Carlos Gimenez said officials were providing ice to 27 senior residence facilities still without power, local media reported.
By then, the main air conditioning system had been down for 53 hours, and within four hours the first of eight residents had died.
Rehabilitation Center officials couldn't immediately be reached for comment. "Right now I just want to figure this out", he said.
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 over 20 in the United States.
As of Friday afternoon, 34 nursing homes were on generator power, 669 had electricity restored, 10 reported being closed and 40 reported post-storm evacuations, the department and AHCA said.
The nursing home has had a list of safety violations and citations, including two for not following generator regulations in 2014 and 2016.
About 1.5 million homes and businesses in Florida and Georgia remained without power on Friday after Hurricane Irma, including 46 of Florida's almost 700 nursing homes caught in the deadly storm's path.
"What we've seen is something extremely tragic", Mr. Gould said.
Scott on Saturday ordered emergency rules requiring all assisted living facilities and nursing homes to obtain a generator within 60 days.
On Twitter, Mr Trump said that first responders had been "great" but he warned there was "much work to do".