By Andrew Innerarity

HOLLYWOOD, Fla. (Reuters) - Eight elderly patients died on Wednesday after being left inside a stifling South Florida nursing home that lost power during Hurricane Irma, prompting a criminal investigation and adding a tragic new dimension to mounting loss of life from the storm.

The overall death toll from Irma climbed to 81 on Wednesday, with several hard-hit Caribbean islands accounting for more than half the fatalities, and officials continued to assess damage inflicted by the second major hurricane to strike the U.S. mainland this year.

Irma killed at least 29 people in Florida, plus seven more in Georgia and South Carolina combined, authorities said.

One of the most powerful Atlantic storms on record, Irma bore down on the Caribbean with devastating force as it raked the northern shore of Cuba last week before barreling into the Florida Keys island chain on Sunday, packing sustained winds of up to 130 miles per hour (215 km per hour). It then plowed north up the Gulf Coast of the state before dissipating.

In addition to severe flooding in areas across Florida and extensive property damage in the Keys, one of the chief hardships facing Floridians has been widespread power outages that initially left more than half of the state without electricity.

Some 4.2 million homes and businesses were still without power on Wednesday in Florida and neighboring states, down from a peak outage tally of 7.4 million customers on Monday.

The power losses had fatal consequences at the Rehabilitation Center at Hollywood Hill, a nursing home in Hollywood, Florida, north of Miami. Three elderly residents were found dead on Wednesday inside the sweltering facility, which had been left without air conditioning, officials said. Five more patients from the nursing home later died at a nearby hospital, they said.

Police said they have opened a probe into possible criminal negligence.

"The building has been sealed off and we are conducting a criminal investigation inside," Hollywood Police Chief Tomas Sanchez told reporters on Wednesday. "It was very hot on the second floor."

Story continues

More than 100 residents at the nursing home were transferred to neighboring branches of Memorial Regional Hospital, along with patients from a nearby facility that also was evacuated due to the police investigation, Hollywood city officials said.

The eight who died ranged in age from 71 to 99, according to the Broward County Medical Examiner's office. The cause of their deaths has yet to be determined.

But most of the surviving patients "have been treated for respiratory distress, dehydration and heat-related issues," Regional Memorial Hospital spokesman Randy Katz told reporters.

Police were first called to the facility at about 4:30 a.m. but authorities did not arrive until after 6 a.m., officials said.

Florida Power & Light said it had provided electricity to some parts of the Hollywood nursing home but that the facility was not on a county top-tier list for emergency power restoration.

"I am going to work to aggressively demand answers on how this tragic event took place," Governor Rick Scott said in a statement. "This situation is unfathomable. Every facility that is charged with caring for patients must take every action and precaution to keep their patients safe."

NEW DAMAGE ESTIMATES

Irma caused about $25 billion in insured losses, including $18 billion in the United States and $7 billion in the Caribbean, catastrophe modeler Karen Clark & Co estimated on Wednesday.

The Florida Keys were particularly hard hit, with federal officials saying that 25 percent of homes were destroyed and 65 percent suffered major damage.

Most residents had left by then and police have barred re-entry to most of the Keys to allow more time to restore electricity and medical service and bring water, food and fuel.

President Donald Trump is due to visit the region on Thursday.

Irma wreaked total devastation in parts of the Caribbean, where at least 43 people have died.

People who fled their homes in hard-hit islands including St. Martin and the U.S. Virgin Islands that were all but cut off from the world for days arrived in San Juan, Puerto Rico, late Tuesday.

Michael Benson, 65, of St. John in the U.S. Virgin Islands, said he lost everything.

"My house, my business, both my vehicles, everything is gone," said Benson, who was stopping in San Juan before continuing to Boston to seek refuge with his wife's brother.

"But we have life. We rode out that horrible storm in a shower that I had reinforced after Hurricane Marilyn," Benson added.

Irma hit the United States about two weeks after Hurricane Harvey plowed into Houston, killing about 60 and causing some $180 billion in damage, mostly from flooding.

(Additional reporting by Zachary Fagenson in Mami, Daniel Trotta in Orlando, Florida, Dan Whitcomb in Los Angeles, Letitia Stein in Detroit, Colleen Jenkins in Winston-Salem, North Carolina, Brendan O'Brien in Milwaukee and Gina Cherelus, Peter Szekeley and Scott DiSavino in New York; Writing by Scott Malone; Editing by Jeffrey Benkoe and Diane Craft)