Almost the entirety of Florida's west coast is under a hurricane or tropical storm warning as the storm and its 230 km/h winds spun just off Mexico's Yucatan peninsula, creeping toward the state.
Milton weakened slightly Tuesday but remained a ferocious storm that could land a once-in-a-century direct hit on the populous Tampa Bay region.
It is expected to bring towering storm surges and turn debris from Helene's devastation 12 days ago into projectiles.
White House Press secretary Karine Jean-Pierre said the travel change was necessary "given the projected trajectory and strength" of the storm.
It was not clear when the trip might be rescheduled. Biden had promised to go to Africa during his term in office, which ends in January.
Milton's centre could come ashore Wednesday night in the Tampa Bay area, which has a population of more than 3.3 million people.
Authorities have ordered evacuations for areas adjacent to the bay.
"You do not have to get on the interstate and go far away," Governor Ron DeSantis said at a Tuesday morning news briefing, assuring residents there would be enough gas to fuel their cars for the trip.
"You can evacuate tens of miles; you do not have to evacuate hundreds of miles away. You do have options."
In Riverview, several drivers waiting in a long line for fuel on Tuesday morning said they have no plans to evacuate.
"I think we'll just hang, you know – tough it out," said Martin Oakes, of Apollo Beach.
"We got shutters up; the house is all ready. So this is sort of the last piece of the puzzle."
Ralph Douglas, of Ruskin, said he, too, will stay put, in part because he worries he would run out of gas trying to return after the storm or get blocked by debris.
DeSantis said the state has been scrambling to remove debris from recent Hurricane Helene.
Authorities in Florida are scrambling to remove debris from Hurricane Helene ahead of another storm. (AP PHOTO)
The state has deployed over 300 dump trucks that are working around the clock and have removed 1200 loads of debris, he said.
After dawn Tuesday, garbage trucks trundled up a nearly deserted street in normally bustling Indian Rocks Beach to gather mounds of debris. Sheriff's deputies used a loudspeaker to urge anyone left to escape as soon as possible.
The National Hurricane Center downgraded Milton early Tuesday to a category four hurricane, but forecasters said it still posed " an extremely serious threat to Florida."
Milton had intensified quickly Monday, becoming a category five storm before being downgraded.
Forecasters warned the sea could surge as high as 4.57 m at Tampa Bay, leading to evacuation orders for beach communities all along the coast.
In Florida, that means anyone who stays is on their own and first responders are not expected to risk their lives to rescue them at the height of the storm.
DeSantis said the state has helped evacuate over 200 health care facilities in Milton's path, and more than 30 county-run shelters are open.
Milton is forecast to remain a dangerous hurricane through landfall and as it crosses central Florida toward the Atlantic Ocean with rainfall totals as high as 20 centimetres possible.
Tampa Bay has not been hit directly by a major hurricane since 1921, and authorities fear luck is about to run out.
