ST. PETERSBURG, Fla. - Hurricane Ian left a path of destruction in southwest Florida, trapping people in flooded homes, destroying the only bridge to Sanibel Island, damaging the roof of a hospital intensive care unit and knocking out power to 2.5 million people as it dumped rain across the peninsula on Thursday.

One of the strongest hurricanes to ever hit the United States threatened catastrophic flooding around the state. Ian’s tropical-storm-force winds extended outward up to 415 miles (665 km), drenching much of Florida and the southeastern Atlantic coast.

With no electricity and patchy cellphone coverage, many calls for help weren’t getting through, even as emergency crews sawed through toppled trees to reach people in flooded homes. “If the line is busy, keep trying,” the Lee County Sheriff’s Office said in a Facebook post early Thursday.

The National Hurricane Center said Ian became a tropical storm over land early Thursday and was expected to regain near-hurricane strength after emerging over Atlantic waters near the Kennedy Space Center later in the day, with South Carolina in its sights for a second U.S. landfall.

A stretch of the Gulf Coast remained inundated by ocean water, pushed ashore by the massive storm. “Severe and life-threatening storm surge inundation of 8 to 10 feet above ground level along with destructive waves is ongoing along the southwest Florida coastline from Englewood to Bonita Beach, including Charlotte Harbor,” the Miami-based hurricane center said.

A chunk of the Sanibel Causeway fell into the sea, cutting off access to the barrier island where 6,300 people normally live. How many heeded mandatory evacuation orders was impossible to know in the storm’s immediate aftermath.

In Port Charlotte, the storm surge flooded a hospital’s emergency room even as fierce winds ripped away part of the roof from its intensive care unit, according to a doctor who works there.

Water gushed down onto the ICU, forcing them to evacuate their sickest patients -- some on ventilators - to other floors, said Dr. Birgit Bodine of HCA Florida Fawcett Hospital. Staff members used towels and plastic bins to try to mop up the sodden mess.

The medium-sized hospital spans four floors, but patients crowded into two because of the damage, and more were expected with people injured from the storm needing help.

“As long as our patients do OK and nobody ends up dying or having a bad outcome, that’s what matters,” Bodine said.

Law enforcement officials in nearby Fort Myers received calls from people trapped in flooded homes or from worried relatives. Pleas were also posted on social media sites, some with video showing debris-covered water sloshing toward the eaves of their homes.

Brittany Hailer, a journalist in Pittsburgh, contacted rescuers about her mother in North Fort Myers, whose home was swamped by 5 feet (1.5 meters) of water.

“We don’t know when the water’s going to go down. We don’t know how they’re going to leave, their cars are totaled,” Hailer said. “Her only way out is on a boat.”

Hurricane Ian turned streets into rivers and blew down trees as it slammed into southwest Florida on Wednesday with 150 mph (241 kph) winds, pushing a wall of storm surge. Ian’s strength at landfall was Category 4, tying it for the fifth-strongest hurricane, when measured by wind speed, ever to strike the U.S.

Ian’s center came ashore more than 100 miles (160 kilometers) south of Tampa and St. Petersburg, sparing the densely populated Tampa Bay area from its first direct hit by a major hurricane since 1921.

Ian dropped to a tropical storm early Thursday over land, but was expected to intensify again once its center moves over the Atlantic Ocean and menace the South Carolina coast Friday at near-hurricane strength before moving inland.

At 5 a.m. Thursday, the storm was about 40 miles (70 km) southeast of Orlando and 35 miles (55 kilometers) southwest of Cape Canaveral, carrying maximum sustained winds of 65 mph (100 kph) and moving toward the cape at 8 mph (13 kmh), the center said.

Hurricane warnings were lowered to tropical storm warnings across the Florida peninsula, with widespread, catastrophic flooding remaining likely, the hurricane center said. Storm surges as high as 6 feet (2 meters) were still forecast for both coasts.

“It doesn’t matter what the intensity of the storm is. We’re still expecting quite a bit of rainfall,” Robbie Berg, senior hurricane specialist with the National Hurricane Center, said in an interview with The Associated Press.

Up to a foot (30 centimeters) of rain forecast for parts of Northeast Florida, coastal Georgia and the Lowcountry of South Carolina. As much as 6 inches (15 centimeters) could fall in southern Virginia as the storm moves inland over the Carolinas, and the center said landslides were possible in the southern Appalachian mountains.

No deaths were reported in the United States from Ian by late Wednesday. But a boat carrying Cuban migrants sank Wednesday in stormy weather east of Key West.

The U.S. Coast Guard initiated a search and rescue mission for 23 people and managed to find three survivors about two miles (three kilometers) south of the Florida Keys, officials said. Four other Cubans swam to Stock Island, just east of Key West, the U.S. Border Patrol said. Air crews continued to search for possibly 20 remaining migrants.

The storm previously tore into Cuba, killing two people and bringing down the country’s electrical grid.

The hurricane’s eye made landfall near Cayo Costa, a barrier island just west of heavily populated Fort Myers. As it approached, water drained from Tampa Bay.

More than 2.5 million Florida homes and businesses were left without electricity, according to the PowerOutage.us site. Most of the homes and businesses in 12 counties were without power.

Sheriff Bull Prummell of Charlotte County, just north of Fort Myers, announced a curfew between 9 p.m. and 6 a.m. “for life-saving purposes,” saying violators may face second-degree misdemeanor charges.

“I am enacting this curfew as a means of protecting the people and property of Charlotte County,” Prummell said.

Life-threatening storm surges and hurricane conditions were possible on Thursday and Friday along the coasts of northeast Florida, Georgia, and South Carolina, where Ian was expected to move inland, dumping more rain well in from the coast, the hurricane center said.

The governors of South Carolina, North Carolina, Georgia and Virginia all preemptively declared states of emergency.

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Associated Press contributors include Christina Mesquita in Havana, Cuba; Cody Jackson and Adriana Gomez Licon in Tampa, Florida; Freida Frisaro in Miami; Anthony Izaguirre in Tallahassee, Florida; Mike Schneider in Orlando, Florida; Seth Borenstein and Aamer Madhani in Washington; Bobby Caina Calvan in New York; Andrew Welsh-Huggins in Columbus, Ohio; Jay Reeves in Birmingham, Alabama, and Alina Hartounian in Phoenix, Arizona.