Wilma's 125 mph winds officially came ashore at 6:30 a.m. at Cape Romano, near the Marco Island-Naples area in Florida. The Keys took a pounding, Marathon is also being hit; trouble may be ahead for West Palm Beach, Fort Pierce and Fort Myers.
Some radio and TV stations have reportedly been knocked off the air at least temporarily. In Marathon, according to CBS Station WFOR-TV, power outages are a problem in some parts of the city.
Wilma strenghtened steadily overnight as it headed toward land, spawning at least three twisters and, off the coast of the Florida Keys - a water spout.
National Hurricane Center Director Max Mayfield has warned that the storm surge in the area south of Marco Island could reach 17 feet.
"This is a very dangerous hurricane," said Mayfield. "People need to stay hunkered down."
Hurricane Wilma's strongest winds began lashing southwest Florida early Monday, battering the coast with torrential rain and pounding waves that threatened flooding in low-lying areas.
The outer eyewall - the ring of 125 mph winds surrounding Wilma's calm eye - is buffeting land in the area where landfall was expected later, likely near Naples and Marco Island.
Wilma, a powerful Category 3 system, got stronger as it neared Florida. The storm's maximum sustained winds were measured at 125 mph - up 10 mph from late Sunday night. A 17-foot storm surge is possible along the southwest coast.
More than 22,600 people are in shelters across the state. But in the low-lying Florida Keys, not even 10 percent of the Keys' 78,000 residents evacuated, Sheriff Richard Roth said.
"We were born and raised with storms, so we never leave," one holdout, Ann Ferguson, explained from her front porch in Key West on Sunday. "What happens, happens. If you believe in the Lord, you don't have no fear."
That could prove to be a mistake: While Wilma is not expected to make landfall over the Keys, the storm could bring a surge of 8 feet to sections of the low-lying island chain.
"They're going to be in deep trouble," warned Billy Wagner, the senior Monroe County emergency management director. Key West was already experiencing minor street flooding early Monday and a wind gust of 76 mph was measured there. Power outages were reported in both the Keys and along the southwest side of the state.
Hurricane-force winds of at least 74 mph extended 90 miles from the center and wind blowing at tropical storm-force reached outward 230 miles, the hurricane center said.
In Miami Lakes, as Wilma spun more than 150 miles away, the blue glow of transformers exploding illuminated the pre-dawn sky. Large signs marking exits on the Palmetto Expressway were already toppled by Wilma's gusts - which were only a tropical storm force at that time.
Wilma's imminent arrival also was announced by at least four tornadoes - including one near Kennedy Space Center at Cape Canaveral - that caused some structural damage, but no injuries.
Once ashore, the fast-moving hurricane is expected to slice northeast across the state at up to 25 mph, with the Atlantic Coast likely to get winds nearly as strong as those hitting the Gulf Coast.
That could spell trouble as far away as coastal Massachusetts, where a wind watch is in effect for late Monday night into Tuesday afternoon. Wilma is creating a Nor'easter whose winds could down trees and power lines and cause property damage. The hurricane itself is expected to track far to the east of New England.
"Less weakening should occur as compared to typical hurricanes moving over land," said forecaster Stacy Stewart of the hurricane center. "Therefore, Wilma is expected to be a Category 2 hurricane when it reaches the Florida east coast."
Thirty-one counties - covering more than half the state's population - are under a tornado watch through Monday morning.
Gov. Jeb Bush asked that Florida be granted a major disaster declaration for 14 counties. Many of the areas bracing for Wilma were hit by hurricanes in the past two years.
The National Guard is on alert, and state and federal officials have trucks of ice and food ready to deploy. The Federal Emergency Management Agency says it is poised to send in dozens of military helicopters and 13.2 million ready-to-eat meals - if they are needed.
Wilma is Florida's eighth hurricane in 15 months and prompted the fourth evacuation of the Keys this year. It earlier battered the Mexican coastline with howling winds and torrential rains.
At least three people were killed in Mexico. Thirteen others died in Jamaica and Haiti, and four bodies were found off Cozumel, though it wasn't clear if they were killed by the storm.
One serious injury was reported in Florida on Sunday: a 12-year-old girl suffered a fractured skull in Wellington when falling hurricane shutters struck her head, said Palm Beach County Sheriff's spokesman Paul Miller.
The girl, Julia Bijuli-Singh, is in critical condition at Delray Medical Center. Her mother is also in the hospital, with a number of cuts.
At the Six L farm worker camp south of Naples - three miles off the ocean and not far from the projected landfall point - workers had nailed plywood to windows and those living in campers fled north. About 90 farmworkers planned to ride out the storm, saying they had no choice.
"We've got to stay. Where would we go? We've got no place to go," said farmworker Salome Rodriguez, 51.
In Europe, crude oil slipped below $60 as traders expected Wilma to avoid already battered Gulf of Mexico oil producing and refining facilities. At least four companies operating in the gulf shut down production platforms.
Weary forecasters also monitored Tropical Depression Alpha, which became the record-breaking 22nd named storm of the 2005 Atlantic season. Alpha, which drenched Haiti and the Dominican Republic on Sunday, was not considered a threat to the United States.