Florida is bracing for monster Hurricane Irma with meteorologists saying Miami is now in "the worst possible position" and that the storm is coming quicker than expected.
CNN meteorologist Tom Sater said that Irma will make landfall late Saturday US time in southern Florida and will be "life threatening".
"It looks like it's shifting, even though it may be just 20 miles (32 kms), it puts Miami right in the worst possible position," Mr Sater said.
Officials are going door-to-door calling on people to evacuate. While 1.4 million Floridians and Georgians are under a mandatory order to evacuate, officials are legally unable to forcibly remove anyone from their homes.
It is estimated at least 18 people are dead after Irma pounded islands in the Caribbean.
Meanwhile the US House voted to send a $US15.3 billion ($19 billion) aid package for Hurricane Harvey victims in Texas through to US President Donald Trump, which will extend US borrowing and fund government through to December 8.
Mr Trump warned Americans to get out of the way of Irma.
"Hurricane Irma is of epic proportion, perhaps bigger than we have ever seen. Be safe and get out of its way, if possible. Federal G is ready!"
Florida Govenor Rick Scott said the call to evacuate had become even more dire.
"We're running out of time. The storm is almost here. If you are in an evacuation zone you need to go now," he said. "This is a catastrophic storm that our state has never seen. We can rebuild your home but we can't rebuild your life."
Hurricane Irma is of epic proportion, perhaps bigger than we have ever seen. Be safe and get out of its way,if possible. Federal G is ready!
Hundreds of thousands of Floridians choked highways to race north, crowded airports and emptying supermarket shelves of bottled water and food, and draining petrol supplies to try to escape what authorities described as a "nuclear storm".
While many were heeding warnings that the entire state faces catastrophic damage, some Aussies were among those considering braving out the approaching hurricane.
Irma yesterday became the longest tropical cyclone in history to sustain wind speeds of 297km an hour. It is the most powerful Atlantic Ocean storm in recorded history.
And yesterday, it was also twice the size of the entire Florida peninsular.
Latest modelling suggests Irma will weaken slightly when it makes landfall in the US, but as a category four storm it will still equal last month's devastating Hurricane Harvey and exceed 2005's Hurricane Katrina.
While Hurricane Jose strengthened to an "extremely dangerous" Category 4 storm on Friday, according to the National Hurricane Centre.
Hurricane Katia has strenghtened to a Category 2 storm in the Gulf of Mexico.
AUSTRALIANS BRACE FOR STORM
Australian cafe owner Spencer Hooker would usually be slinging meat pies and flat whites, but yesterday he filled sandbags and used plywood to board up windows.
"There's a lot of uncertainty," Mr Hooker, 36, who has four Kookaburra Coffee cafes in St Augustine, on the northeast coast of Florida, told AAP.
The hurricane has killed at least ten people as it crashed through Caribbean islands including St Martin, Puerto Rico and the British Virgin Islands. Mr Hooker and other Australians were waiting until Friday (ET) to get a better read on what path Irma would likely take before deciding whether to evacuate.
"One of my baristas is from Noosa and his wife is eight months pregnant," Mr Hooker said.
The couple hopes to stay in the area where their doctor and hospital is, but are prepared to evacuate.
Gavin Caddy, an Australia lawyer in Fort Lauderdale on Florida's southeast coast, is driving 240km north to be with friends in the central Florida city of Sebring.
"You can't play games with this," Mr Caddy said.
"It's as wide as the state of Florida so the chances are it will hit the entire state and some areas are worse than others.
"There is nowhere in south Florida that is safe as far as I'm concerned."
Another Australian in Fort Lauderdale, yacht broker David Nichols, is staying at his home that is eight kilometres inland on the New River.
He spent Thursday drilling plywood across windows and has stocked his fridges and freezer "with plenty of water, beer wine and spirits".
He also stocked up on an "Aussie survival pack" including TimTams, two types of Bundy rum and some Vegemite.
PRESIDENTS BAND TOGETHER TO HELP HARVEY/IRMA VICTIMS
All five living former US presidents have issued a joint One America Appeal for donations to support the staggering recovery needs from Hurricane Harvey that hit Texas.
Now that Hurricane Irma has damaged Puerto Rico and is closing in on Florida, the presidents are expanding the appeal to help its victims as well.
A website for tax-deductible donations related to both storms is now live at OneAmericaAppeal.org.
A special restricted account has been established through the George H.W. Bush Presidential Library Foundation to collect and quickly distribute donations to ensure 100 cents out of every dollar goes to assist hurricane victims.
The Carter Centre says Harvey has displaced more than one million people and caused an estimated $US180 billion in damage over its 482-kilometre path of destruction.
Some forecasters have predicted that Irma's economic toll could be even greater.
Mr Trump tweeted that he was proud to stand with past presidents.
"We will confront ANY challenge, no matter how strong the winds or high the water. I'm proud to stand with Presidents for #OneAmericaAppeal," he tweeted.
We will confront ANY challenge, no matter how strong the winds or high the water. I’m proud to stand with Presidents for #OneAmericaAppeal.