The UK is racing to provide support for Britons stranded in the path of Hurricane Irma as it bears down on the US mainland with increased strength.
The historic storm has regained its category five status after data showed its windspeeds had risen as it tears past Cuba.
Prime Minister Theresa May said work was taking place with US authorities to ensure British expats and tourists in Florida are protected as millions of locals and visitors flee to safety.
Officials in the Sunshine State warned "time is running out" to escape danger areas, calling on anyone remaining there to follow the mandatory evacuation orders.
The low-lying Florida Keys will be struck first when Irma arrives on Sunday and authorities are reportedly considering withdrawing emergency teams from the islands.
Meanwhile the last flights from major airports in Miami and Fort Lauderdale left on Friday evening and the last services from Orlando and Tampa international airports will be on Saturday evening.
Among those hoping to be on one of the remaining departures was Cathy Robson, the mother of British tennis star Laura Robson.
She tweeted to British Airways: "Is TPA (Tampa) to LGW (Gatwick) still on tmrw?? Cant get through on the phone. My mum's been evacuated & planning on staying by the airport."
The National Hurricane Centre (NHC) has forecast Irma will reach the Keys and southern Florida on Sunday morning, bringing devastating winds, rain and storm surges up to 12ft high.
Hopes the storm had weakened were dashed when an Air Force Reserve Hurricane Hunter aircraft found sustained windspeeds had increased to nearly 160mph, with gusts higher still.
Forecasters had further dire news for some of the Caribbean islands reeling in Irma's wake as data suggested Hurricane Jose was "almost a category five" with sustained winds up to 155mph.
Jose is expected to come close to the devastated northern Leeward Islands on Saturday.
The NHC has issued hurricane warnings for the Commonwealth islands of Barbuda and Antigua and British territory of Anguilla, while the British Virgin Islands are on tropical storm watch.
Irma claimed at least 20 lives and left thousands of people homeless when it smashed into the region on Wednesday.
Five of the 22 people reported to have died during Irma are said to have come from the British Virgin Islands and Anguilla.
Aid and expertise is being provided to Britain's territories in the region in a £32 million government cash injection.
Following a meeting of the Government's emergency Cobra committee, Mrs May said: "I heard directly from our consul general in Miami about the support that is being given to British nationals living in Florida and also British tourists in Florida.
"We are, of course, working with the US authorities to ensure that every support is available and everything can be done before Hurricane Irma reaches Florida."
Life-threatening wind, rain and a storm surge are expected in the Turks and Caicos Islands, another British territory, into Saturday, after it was "pummelled" by Irma on Thursday night.
Off the coast of the British Virgin Islands, the captain of the naval vessel spearheading Britain's relief efforts described scenes of destruction.
Stephen Norris, commanding officer of Royal Fleet Auxiliary Mounts Bay, told the Press Association: "I haven't seen anything on the scale of what we have seen here.
"It is one of those storms which I think defies all expectations."
Engineers, marines and medics are being carried on board the ship, which delivered six tonnes of supplies to Anguilla and carried out repair work before moving to the British Virgin Islands.
Captain Norris said: "We will be here as long as it takes. I will stay here as long as I possibly can to support the islands."
The Department for International Development said a further 20 million tonnes of aide was en route to the disaster zone.
In Whitehall, accusations continued to be levelled at the Government for its handling of the crisis.
Chairmen of the Commons Foreign Affairs and International Development committees, Tom Tugendhat and Stephen Twigg, said Britain's response has been "found wanting".
In a letter to Foreign Secretary Boris Johnson and International Development Secretary Priti Patel, they wrote: "While we welcome the increase in funding for disaster relief in the British Overseas Territories to £32 million and the fact that personnel, equipment and the RFA Mounts Bay were dispatched to the area before the hurricane struck, arriving in Anguilla the day after its devastation, we are concerned that many in the UK's overseas territories in the Caribbean are still in grave need."
The Foreign Office has set up a hotline for people affected by the disaster and for people whose loved ones may be affected, on 020 7008 0000.