The US National Hurricane Center described Milton as a “catastrophic” and “dangerous” major hurricane, packing maximum sustained winds of 260km/h, putting it at the highest level on the five-step Saffir-Simpson scale.
Weather conditions were expected to start deteriorating in the afternoon, it said in an advisory.
Officials from US President Joe Biden to Tampa Mayor Jane Castor warned people in evacuation zones to get out or risk death.
Michael Tylenda, who was visiting his son in Tampa, said he was heeding that advice.
“If anybody knows anything about Florida, when you don’t evacuate when you’re ordered to, you can pretty much die,” Tylenda said.
“They’ve had a lot of people here stay at their homes and they end up drowning. It’s just not worth it. You know, the house can be replaced. The stuff can be replaced. So it’s just better to get out of town.”
While wind speeds could drop and downgrade Milton to a lesser category, the size of the storm was growing, putting ever more coastal areas in danger.
In its latest advisory, the NHC said Milton was expected to turn to the east-northeast and east on Thursday and Friday.
Early on Wednesday, the eye of the storm was about 480km southwest of Tampa.
Milton was expected to maintain hurricane strength as it crosses the Florida peninsula, posing storm surge danger on the state’s Atlantic Coast as well.
Milton became the third-fastest intensifying storm on record in the Atlantic, growing from a category one to a category five in less than 24 hours.
“These extremely warm sea surface temperatures provide the fuel necessary for the rapid intensification that we saw taking place to occur,” said climate scientist Daniel Gilford of Climate Central, a non-profit research group.
“We know that as human beings increase the amount of greenhouse gases in the atmosphere, largely by burning fossil fuels, we are increasing that temperature all around the planet.”
More than a dozen coastal counties issued mandatory evacuation orders, including Tampa’s Hillsborough County.
Pinellas County, which includes St Petersburg, ordered the evacuation of more than 500,000 people.
Lee County said 416,000 people lived in its mandatory evacuation zones.
Mobile homes, nursing homes and assisted living facilities also faced mandatory evacuation.
In Fort Myers, mobile home-dweller Jamie Watts and his wife took refuge in a hotel after losing their previous trailer to Hurricane Ian in 2022.
“My wife’s happy. We’re not in that tin can,” Watts said.
“We stayed during Ian and literally watched my roof tear off my house and it put a turmoil in us. So this time I’m going to be a little safer.”
Bumper-to-bumper traffic choked roads leading out of Tampa on Tuesday, when about 17% of Florida’s nearly 8000 petrol stations had run out of fuel, according to fuel markets tracker GasBuddy.
