Millions are facing the possibility of being evacuated as the storm swirls towards the US mainland - and is expected to roar into Florida later today.

The fire service said "if you remain there, you could die", while there have been warnings that debris caused by Hurricane Helene could be picked up and turned into projectiles in the strong winds.

The storm was downgraded to a category 4 on Tuesday but later reclassified again as category 5 - the strongest category available.

Category 5 storms mean wind speeds greater than 156 mph, which are expected to cause "catastrophic damage".

What else do we know about the hurricane so far and what does it mean for people in its path?

Where is the hurricane now and when will it hit the US?

Milton is currently heading towards the US at 12mph (19kph) and is sucking energy from the Gulf of Mexico's warm water.

It is expected to have winds of up to 129mph when it hits the shores in the Tampa Bay area on Florida's west coast on Wednesday, and has already sustained maximum winds of 180mph (285kph).

The region, home to more than three million people, has not experienced a direct hit by a major hurricane in more than a century.

The storm is also threatening Mexico's Yucatan Peninsula, where more than one million people have been ordered to evacuate.

On the upside, scientists expect Milton to weaken slightly before landfall, and its path through central Florida will spare the states devastated by Helene less than two weeks ago.

What is the storm surge warning?

As of Tuesday morning, Tampa Bay is under both a hurricane warning and a storm surge warning, as the National Hurricane Center (NHC) forecasts that it could be inundated with surges between three to four metres high.

The NHC said that peak storm surge levels would be between the Anclote River and Englewood, a stretch of about 100 miles that includes Tampa and various islands and keys.

"The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline," an update said.

What measures are being taken to protect residents?

Hundreds of thousands of residents in communities along the western Gulf Coast were subject to evacuation orders.

In Florida, this means that first responders are not expected to risk their lives during a storm to rescue anyone who chooses to stay.

"If you remain there, you could die, and my men and women could die trying to rescue you," Hillsborough Fire Rescue Chief Jason Dougherty said.

In a news conference this afternoon, Governor Ron DeSantis said the authorities are amassing up to 1.2 million fuel reserves and are ensuring that critical infrastructure - including hospitals and waste water treatment centres - have flood protection systems.

"We've never had this many resources prior to a storm," he said.

There was significant traffic congestion on Monday as Tampa Bay residents escaped to safer areas in the north towards the Florida Panhandle or southeast to Fort Lauderdale and Miami.

President Joe Biden approved an emergency declaration for Florida, and US Representative Kathy Castor said 7,000 federal workers were on hand to help in one of the largest mobilisations of federal personnel in history.

"This is the real deal here with Milton," Tampa mayor Jane Castor told a news conference on Monday. "If you want to take on Mother Nature, she wins 100% of the time."

Meanwhile, Mexican officials were using buses to evacuate people from low-lying towns and cities.

How powerful is Hurricane Milton?

Milton was downgraded to a Category 4 hurricane earlier this morning, but the NHC said it still posed "an extremely serious threat to Florida".

Mr DeSantis described it as a "really significant" hurricane.

The storm intensified quickly on Monday, becoming a Category 5 storm in the afternoon with maximum sustained winds of 180 mph (285 kph) before being downgraded.

The strongest Atlantic hurricane on record is Allen in 1980, which reached wind speeds of 190mph (306 kph) as it moved through the Caribbean and Gulf before striking Texas and Mexico.

Milton became the third-fastest intensifying storm on record in the Atlantic Ocean, the US National Hurricane Centre said, and its path from west to east was also unusual, as Gulf hurricanes typically form in the Caribbean Sea and make landfall after traveling west and turning north.

Hasn't the US just had a hurricane?

Yes, the area Hurricane Milton is forecast to hit was already devastated by Hurricane Helene just 12 days ago.

Helene, which also affected Georgia, North and South Carolina, Tennessee, Virginia and Kentucky, killed at least 230 people and caused devastating flooding and destruction.

Helene is also set to have a massive effect on Milton - Florida residents are scrambling to clear debris of the initial storm, as it could turn into projectiles when Hurricane Milton makes landfall, Sky's US partner network NBC News reports.

What if I have travel plans in Florida?

Tampa International Airport said it planned to stop flights at 9am local time on Tuesday. The airport posted on X that it is not a shelter for people or their cars.

Meanwhile, St Pete-Clearwater International Airport said it is in a mandatory evacuation zone and will close after the last flight leaves on Tuesday.