More than one million customers have lost power in Florida as Hurricane Ian made landfall as Category 4 storm, a tracking website recorded, with the number expected to rise as high winds, heavy rain and floods take their toll.
Of 11 million customers tracked in Florida, 1,040,000 were suffering outages, PowerOutages.us reported on Wednesday.
The National Hurricane Center said the eye of the "extremely dangerous" hurricane slammed into the barrier island of Cayo Costa, west of the city of Fort Myers, at 3:05 pm.
Dramatic TV footage showed churning water submerging roads and sweeping away cars as the hurricane pounded the coastal city of Naples to the south of Fort Myers.
The NHC said Ian was packing maximum sustained winds of 240 kilometres per hour when it made landfall and was already "causing catastrophic storm surge, winds and flooding in the Florida peninsula."
Ian is expected to affect several million people across Florida and in the southeastern states of Georgia and South Carolina and may have already claimed its first casualties.
One for the ages
As hurricane conditions spread, forecasters warned of a looming once-in-a-generation calamity.
"This is going to be a storm we talk about for many years to come," said National Weather Service director Ken Graham. "It's a historic event."
Punta Gorda, north of Fort Myers, was being pounded by torrential rain and streets emptied as the howling winds ripped fronds off of palm trees and shook electricity poles.
Some 2.5 million people were under mandatory evacuation orders in a dozen coastal Florida counties, with several dozen shelters set up, and voluntary evacuation recommended in others.
For those who decided to ride out the storm, authorities stressed it was too late to flee and that residents should hunker down and stay indoors.
With winds of 241 kph as it made landfall, Ian is just 11.26 kph shy of Category 5 intensity — the strongest on the Saffir-Simpson scale.
Airports in Tampa and Orlando stopped all commercial flights, and 850,000 households were already without power.
But that was a "drop in the bucket" compared with the outages expected over the next 48 hours, Florida Governor Ron DeSantis said.
"This is going to be a nasty, nasty day, two days," he added.
With up to 61 centimetres of rain expected to fall on parts of the so-called Sunshine State and a storm surge that could reach devastating levels of 3.6 to 5.5 metres above ground, authorities were warning of dire emergency conditions.
"This is a life-threatening situation," the NHC warned.
The storm was set to move across central Florida before emerging in the Atlantic Ocean by late Thursday.
Ian a day earlier had plunged all of Cuba into darkness after battering the country's west as a Category 3 storm and downing the island's power network.
At least two people died in Pinar del Rio province, Cuban state media reported.
In the United States, the Pentagon said 3,200 national guardsmen were called up in Florida, with another 1,800 on the way.
As the climate crisis warms the ocean's surface, the number of powerful tropical storms, or cyclones, with stronger winds and more precipitation is likely to increase.