FORT MYERS, Florida — A weakening but still potent Hurricane Irma lashed Florida’s Gulf Coast on Sunday with tree-bending winds, pounding rain and surging surf, leaving more than 3 million homes and businesses without power statewide while flooding streets and swaying skyscrapers in Miami.

Forecasters warned that Irma remained extremely dangerous as the monster storm toppled trees and power lines, peeled tiles off roofs and threatened coastal areas with storm surges of up to 15 feet. Tornadoes were also spotted through the southern part of the state.

Hours after barreling across the resort archipelago of the Florida Keys, the storm crept up the western shore of the Florida Peninsula to make a second landfall at Marco Island around 3.35 p.m., about a dozen miles south of the upscale beach town of Naples on the Gulf of Mexico.

Irma’s center came ashore not long after it was downgraded to a Category 3 storm from a Category 4 on the five-point Saffir-Simpson hurricane scale, with maximum sustained winds of 120 mph.

A few hours later, it was downgraded again to Category 2, with maximum sustained wind gusts of 110 mph, the National Hurricane Center reported in Miami.

Some 6.5 million people, about a third of the state’s population, had been ordered to evacuate southern Florida as the storm approached. An estimated 170,000 people were lodged in some 650 emergency shelters as of early evening, according to the Florida Division of Emergency Management.

“This is a life-threatening situation,” Gov. Rick Scott told a news conference. Curfews were declared Sunday evening for the Gulf Coast cities of Tampa and St. Petersburg as several Florida counties reported arrests of looters taking advantage of homes left vacant by evacuations.

The storm killed at least 28 people as it raged through the Caribbean en route to Florida. On Sunday, Irma claimed its first U.S. fatality — a man found dead in a pickup truck that had crashed into a tree in high winds in the town of Marathon, in the Keys.

The storm’s westward tilt as it advanced on Florida put a string of Gulf Coast cities at greatest risk and spared the densely populated Miami area the full force of its wrath. The state’s biggest city, situated about 100 miles east of Irma’s core, was anything but unscathed.

Miami apartment towers swayed in the high winds, two construction cranes were toppled, and small, white-capped waves could be seen in flooded streets between Miami office towers.

Last week, Irma ranked as one of the most powerful hurricanes ever documented in the Atlantic, one of only a handful of Category 5 storms known to have packed sustained winds at 185 mph or more.

Before turning on Florida, the storm pummeled Cuba with 36-foot-tall waves after ravaging several smaller Caribbean islands. It was expected to move along or over Florida’s western coast through evening.

Irma is expected to cause billions of dollars in damage to the third-most-populous U.S. state, a major tourism hub with an economy that generates about 5 percent of U.S. gross domestic product.

At least 3 million Florida homes and businesses had lost power, according to Florida Power & Light and other utilities.

Waves poured over a Miami seawall, flooding streets waist-deep in places around Brickell Avenue, which runs a couple of blocks from the waterfront through the financial district and past consulates. High-rise apartment buildings were left standing like islands in the flood.

One woman in Miami’s Little Haiti neighborhood delivered her own baby because emergency responders were unable to reach her, the city of Miami said on Twitter. Mother and infant were later taken to a hospital, it said.

Cranes atop two downtown Miami high rises under construction collapsed in the face of 100 mph winds Irma ripped through the city.

Soon after one of the cranes collapsed, the chief executive of the company developing the building told Reuters he was attending the U.S. Open tennis tournament in New York when the accident occurred and had just learned about it.

“This particular crane, some of it was taken down,” Jorge Perez, chief executive of The Related Group, Miami’s largest developer, said by telephone. “They were surprised that it went down because they felt it was one of the more secure cranes, so we’re right on it.”

A video posted on Twitter showed the crane’s boom dangling above the unfinished building.

No injuries were reported in either of the collapses, and investigations would begin after the storm cleared, officials said.

Deme Lomas, who owns Miami restaurant Niu Kitchen, said he saw one of the cranes dangling from the top of a building.

“We feel the building swaying all the time,” Lomas said in a phone interview from his 35th-floor apartment. “It’s like being on a ship.”

On Marco Island, home to about 17,000 residents, 67-year-old Kathleen Turner and her husband rode out the storm on the second floor of a friend’s condominium after failing to find a flight out. She feared for her canal-facing home.

“I’m feeling better than being in my house, but I’m worried about my home, about what’s going to happen,” Turner said.

“I am prepared to say goodbye to my things, and that is hard,” Allison McCarthy Cruse, 42, said as she huddled with seven other adults, three children and seven dogs in the home of a neighbor just blocks from the water in St. Petersburg. She said she feared the roof on her own house might not survive.

Irma comes just days after Hurricane Harvey dumped record-breaking rain in Texas, causing unprecedented flooding, killing at least 60 people and an estimated $180 billion in property damage. Almost three months remain in the Atlantic hurricane season, which runs through November.

President Donald Trump called Hurricane Irma “some big monster,” adding that he wanted to go to Florida very soon and praising emergency officials for their efforts to protect people.

“The bad news is that this is some big monster,” Trump told reporters at the White House, saying damage from the storm would be very costly.

“Right now, we are worried about lives, not cost,” Trump said after returning from Camp David, the presidential retreat in Maryland where he monitored the storm and met with his Cabinet.

“I hope there aren’t too many people in the path,” he said. “You don’t want to be in that path.”

The U.S. House of Representatives canceled votes scheduled for Monday because of the hurricane.

Trump, acting on Scott’s request, approved a major disaster declaration for Florida on Sunday, freeing up emergency federal aid in response to Irma.

American Airlines said late Sunday it will resume limited operations at its Miami International Airport hub on Monday evening, but it will take days before the airline returns to normal operations.

The Fort Worth, Texas, airline canceled all flights at the airport starting on Friday evening in anticipation of Irma, along with flights at three other south Florida airports. All American flights remain canceled through Monday at 12 other Florida airports, as well as Hilton Head, South Carolina, and Savannah, Georgia.