Hurricane Maria has intensified into a "potentially catastrophic" category five storm as it continues on a collision course with Caribbean islands already battered by Irma.
The US National Hurricane Centre (NHC) said the hurricane, which has recorded winds of more than 160mph, is likely to remain "extremely dangerous" when it approaches the British Virgin Islands (BVI).
Emergency steps are being undertaken on the BVI to prepare for the looming onslaught, although an official coordinating the operation has warned the islands had been "weakened" by Irma and the situation "doesn't look good".
Relief workers are racing to secure debris left strewn across the islands that have the potential to make the coming hurricane "more hazardous" if they are picked up by high winds.
Another British overseas territory, Montserrat, has been issued with a hurricane warning amid fears Maria could bring a devastating storm surge, while torrential rain could trigger deadly flash floods.
UK International Development Secretary, Priti Patel, said the Government is under no illusion about the possible impact of the strengthening hurricane and said they are taking steps to prepare communities.
The British Foreign and Commonwealth Office is advising against all travel to the BVI, warning residents to identify shelter "immediately" and be ready to take cover when the hurricane approaches.
Following a similar path to Irma, Maria's "intense" centre made landfall with Dominica on Monday and the hurricane is expected to reach the British Virgin Islands on Tuesday night and into Wednesday.
Brigadier John Ridge, the second in command of the UK's Joint Task Force, said whichever direction the hurricane goes, "it is bad".
"They are either going to get the wind, which will pick up all the debris that is lying around," he said.
"And also, irritatingly, where they have made progress in getting covers over the houses and power lines up, it will potentially damage that again.
"Or they get a huge amount of rain, which is also bad because of the blockages in the drainage channels - so the potential for some quite serious flooding as well.
"Whatever happens, it doesn't look good sadly."
British Foreign Office officials have also warned against all but essential travel to Montserrat, where residents voiced concerns that the hurricane will strike the island from the south, creating a "very serious" situation.
Meanwhile the NHC has issued a hurricane watch, meaning hurricane conditions are expected somewhere within the area, for the island of Anguila, another island badly affected by hurricane Irma.
Hurricane warnings have also been issued for Guadeloupe, St Kitts and Nevis, the US Virgin Islands and Puerto Rico where a state of emergency has been declared amid fears of a direct hit.
Dominica's President Roosevelt Skerrit said the hurricane had wrought "widespread devastation" and the islanders had "lost all what money can buy and replace".
He said in a Facebook post: "The winds have swept away the roofs of almost every person I have spoken to or otherwise made contact with."
Up to 15in (38cm) of rain is predicted to fall as Maria barrels across the Caribbean, with "isolated maximum amounts of 20in (51cm)" expected to deluge the British Virgin Islands.
In Anguilla up to 8in (20cm) could be recorded. The National Hurricane Centre has warned that "rainfall on these islands could cause life-threatening flash floods and mudslides".
Brigadier Ridge said the combination of tidal surges and flooding on the British Virgin Islands is something that is worrying the governor, Gus Jaspert.
"They had an hour's rain a few days ago and that created four foot of flooding, so if you get potentially 12 hours of rain you can imagine how much worse that will be," he added.
Hurricane Maria arrived in the region less than two weeks after Hurricane Irma, one of the most powerful storms in decades, unleashed devastation.
Ms Patel said British troops, police and aid experts are "working relentlessly" to help the victims of Irma, and that they are now being tasked with also preparing for the impact of Maria.
"We are under no illusions about the possible impact of Hurricane Maria and are taking every measure possible to prepare communities which have already been devastated by Hurricane Irma," she said.
More than 1,300 UK troops are currently deployed in the region, and were sent to help with relief and repair work after Hurricane Irma caused chaos.
An additional 42-strong military resilience team has also been deployed to the British Virgin Islands ready to offer support and assistance after Maria has hit.
HMS Ocean, which is carrying another 60 tonnes of aid to complement the 75 tonnes of DfID relief items which have already arrived, will drop anchor in the region this weekend.
Brig Ridge said that alongside the aid the vessel is carrying, it will also bring specialists and a "whole lot of helicopters" into the operational mix.
After docking in the British Virgin Islands, he said HMS Ocean will then move up to Turks and Caicos and could, if needed, divert to Anguilla.