The storm hit the coast on Wednesday night as a category-three hurricane with maximum sustained winds of 195km/h near Siesta Key, the US National Hurricane Center said.
By early Thursday, wind speeds reduced to a still-dangerous 150km/h, dropping Milton to a category-one hurricane, still packing heavy rain and damaging storm surges.
The hurricane was about 75km west-southwest of Cape Canaveral, home to NASA's Space Force Station.
A flash flood emergency was in effect for the Tampa Bay area including the cities of Tampa, St Petersburg and Clearwater, the hurricane centre said, with St Petersburg already receiving 422 millimetres of rain on Wednesday.
[1:00am EDT Oct 10] Damaging winds from Hurricane — National Hurricane Center (@NHC_Atlantic) #Milton are now reaching the Florida East Coast, and a Flash Flood Emergency continues over portions of west-central Florida.https://t.co/LQEVorqXZH pic.twitter.com/8LutJPED17October 10, 2024
The eye of the storm made landfall in Siesta Key, a barrier island town of some 5400 off Sarasota about 100km south of the Tampa Bay metropolitan area, which is home to more than three million people.
Governor Ron DeSantis said he hoped Tampa Bay, once seen as the potential bull's eye, could dodge major damage and that the worst of the predicted storm surge could be avoided thanks to the landfall coming before the high tide.
Forecasters said sea water could still rise as high as four metres.
DeSantis reported Milton had also spawned at least 19 tornadoes caused damage in numerous counties, destroying about 125 residences, most of them mobile homes.
"At this point, it's too dangerous to evacuate safely, so you have to shelter in place and just hunker down," DeSantis said.
At least two deaths were reported at a retirement community following a suspected tornado in Fort Pierce on the eastern coast of Florida, NBC News reported, citing St Lucie County Sheriff Keith Pearson.
Pearson estimated 100 homes were destroyed in the county where some 17 tornadoes touched down, NBC said.
Florida is suffering even more storm after already being battered by Hurricane Helene two weeks ago. (AP PHOTO)
More than two million homes and businesses in Florida were without power, according to PowerOutage.us.
The storm was expected to cross the Florida peninsula overnight and emerge into the Atlantic, still with hurricane force, on Thursday.
Milton is forecast to maintain hurricane intensity while crossing Florida later on Thursday morning but after moving into the Atlantic it is likely to gradually lose tropical characteristics and slowly weaken, the hurricane centre said.
In a state already battered by Hurricane Helene two weeks ago, as many as two million people were ordered to leave, and millions more live in the projected path of the storm.
Much of the southern US experienced the deadly force of Hurricane Helene as it cut a swathe of devastation through Florida and several other states.
Both storms are expected to cause billions of dollars in damage.
US President Joe Biden was briefed by emergency authorities on the initial impacts of the hurricane, according to a White House statement.
Hurricane Milton hit the Florida coast as a category-three storm with winds of 195km/h. (EPA PHOTO)
While human evacuees jammed the highways and created fuel shortages, animals including African elephants, Caribbean flamingos and pygmy hippos were riding out the storm at Tampa's zoo.
Nearly a quarter of Florida's petrol stations were out of fuel on Wednesday afternoon.
The Federal Emergency Management Agency had moved millions of litres of water, millions of meals and other supplies and personnel into the area.
None of the additional aid would detract from recovery efforts for Hurricane Helene, the agency's administrator, Deanne Criswell, said earlier on Wednesday.
Trucks have been running 24 hours a day to clear mounds of debris left behind by Helene before Milton potentially turned them into dangerous projectiles, DeSantis said.
About 9000 National Guard personnel were deployed in Florida, ready to assist recovery efforts, as were 50,000 electricity grid workers in anticipating of widespread power outages.
Search-and-rescue teams were prepared to head out as soon as the storm passed, working through the night if needed, DeSantis said.
