Besides the nursing home deaths, at least 14 deaths in Florida have been tied to the storm and its aftermath, with six more in SC and Georgia.
Officials say conditions in the nursing home were sweltering because air conditioning had been knocked out by the storm.
Across Florida, powerless residents are forced to deal with spoiled food in warm refrigerators, cellphones losing battery and service, and high temperatures increasing risk of heatstroke for the young and old.
Irma killed 82 people in the Caribbean islands, including the US Virgin Islands and Puerto Rico.
Power outages continue to plague the state, with 4.4 million customers still without power as of Wednesday morning, according to the Florida Division of Emergency Management. Broward County Mayor Barbara Sharief said government officials had requested that power companies prioritise senior citizen communities before the hurricane hit.
The state of Florida responded by preventing the facility from admitting new patients and evacuating the rest of its residents.
Hurricane Irma slammed into Southwest Florida last weekend, destroying buildings and snapping trees after causing more extensive damage on the Florida Keys. They called 911. They said there's no air conditioning.
The eight victims ranged in age from 70 to 99.
"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.
Before it reached Florida, Hurricane Irma cut a destructive swath through the Leeward Islands.
The storm, which was moving into southern Georgia, was packing maximum sustained winds of 97 km/h, according to the US National Hurricane Center on Monday.
The governor said he has ordered a probe by state authorities, and Sanchez confirmed a criminal investigation has been launched.
"Although the details of these reported deaths are still under investigation, this situation is unfathomable", he said.
Had they had other financial means, Mitchell says, the family would have taken Wilson out of the rehabilitation center long ago if it weren't for their insurance and the inability to choose where they wanted to go. Our newsroom has been inundated with calls, emails and social media posts about Florida Power and Light's response to the on-going power crisis.
"I wished I had just said you know i should just go and check on her, just make sure she's okay but when you put something into professional people's hands you think that everything's gonna be okay", said Eatherly's friend Linda Horton.
Elsewhere around the state, a Coral Gables apartment building was evacuated after authorities determined a lack of power made it unsafe for elderly tenants.