Elsewhere in South Florida, other alarms were sounded for older residents.
The nearby Larkin Community Hospital was also evacuated.
The entire facility -which has two wings- was evacuated.
Florida officials have made restoring electricity to the millions who have lost power a priority and tens of thousands of utility company workers, many from out of state, are engaged in the huge effort.
Irma's death toll in Florida rose to at least 25 by Wednesday morning.
During a news conference, Thursday morning, City of Hollywood spokesperson Raelin Storey confirmed, "The initial investigation has determined the facility had some power".
Governor Rick Scott said he was "absolutely heartbroken" to learn of the deaths of the elderly retirees.
Broward County Mayor, Barbara Sharief informed that three people had already died inside the nursing home and the rest five died in hospital's emergency room.
A total of eight others died in Georgia and the Carolinas. He also said investigators will look into how many windows were open. Officials say the water will likely rise further in the coming days. "But nobody from the facility has told me anything yet".
Television footage showed rescue crews arriving at the facility shortly after 7.30am on Wednesday and patients sitting outside in wheelchairs.
Hollywood police carried out a search warrant of the Hollywood Hills home as the criminal investigation into this tragedy moves forward.
One person was found dead and three others were taken to the hospital for carbon monoxide poisoning in Daytona Beach, caused by fumes from a gas generator. County officials released documents showing that the Hollywood facility was in compliance with that regulation and that it held a hurricane drill with its staff in October.
In the immediate aftermath of the storm, roughly 65 percent of all homes and businesses in the state were in the dark. At least 37 people were killed in the Caribbean. Although the deaths of those will come under Hurricane Irma's devastating effect, still many people believe that the unfortunate incidence could have been avoided.