• Hurricane Milton makes landfall in Florida as Category 3 hurricane.
• Deadly hurricane prompts flash flood emergency for Tampa Bay.
• US state prepared to engage in search, rescue missions overnight.
  

Hurricane Milton made landfall on Florida's west coast on Wednesday, whipping up deadly tornadoes, destroying homes and provoking flash floods and power outages as it began its eastward march across the state.

The storm made landfall around 8:30pm EDT as a Category 3 hurricane with maximum sustained winds of 195 kilometres per hour near Siesta Key, the United States National Hurricane Center said.

By 11pm EDT, wind speeds had reduced to 165 kph, dropping Milton to a Category 2 hurricane, nonetheless still considered extremely dangerous. The eye of the storm was 120 kilometres southwest of Orlando in the center of the state.

A flash flood emergency was in effect for the Tampa Bay area including the cities of Tampa, St Petersburg and Clearwater, the hurricane center said, with St Petersburg already receiving 422 milimetres of rain on Wednesday.

The eye of the storm came ashore in Siesta Key, a barrier island town of some 5,400 off Sarasota about 100 km south of the Tampa Bay metropolitan area, which is home to more than three million people.

With the storm coming ashore before high tide, Governor Ron DeSantis said he hoped the west coast of Florida could avoid the worst of the predicted storm surge. Forecasters said seawater could rise as high as four metres.

Even so, Milton had already spawned at least 19 tornadoes. Multiple fatalities were reported at a retirement community following a suspected tornado in Fort Pierce on the eastern coast of Florida, ABC News reported, citing St Lucie County Sheriff Keith Pearson.

The tornadoes caused damage in numerous counties, and destroyed around 125 homes, most of them mobile homes, DeSantis said.

More than 1.3 million homes and businesses in Florida were without power.

"At this point, it's too dangerous to evacuate safely, so you have to shelter in place and just hunker down," DeSantis said upon announcing the landfall.

The storm was expected to cross the Florida peninsula overnight and emerge into the Atlantic, still with hurricane force, on Thursday.

Once past Florida, it should weaken over the western Atlantic, possibly dropping below hurricane strength on Thursday night, but will nonetheless pose storm-surge danger on the state's Atlantic coast as well.

Tropical storm force winds were engulfing much of the state. At sea, the hurricane created waves close to 8.5m high, the National Oceanic and Atmospheric Administration said.

In a state already battered by Hurricane Helene two weeks ago, as many as two million people were ordered to evacuate, 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 swath of devastation through Florida and several other states. Both storms are expected to cause billions of dollars in damage.

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 will detract from recovery efforts for Hurricane Helene, the agency's administrator, Deanne Criswell, said earlier on Wednesday.

About 9,000 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, DeSantis said.

Search-and-rescue teams were prepared to head out as soon as the storm passes, working through the night if needed, DeSantis said.

"It's going to mean pretty much all the rescues are going to be done in the dark, in the middle of the night, but that's fine. They're going to do that," DeSantis said.

Nineteen hospitals were evacuated, the Florida Hospital Association said. Mobile homes, nursing homes and assisted-living facilities faced mandatory evacuation.

Milton became the third-fastest intensifying storm on record in the Atlantic, growing from a Category 1 to a Category 5 in less than 24 hours.