Haiti and the Turks and Caicos islands have been preparing for the arrival of Hurricane Irma, which has left a trail of destruction across the Caribbean.
Poverty-stricken Haiti is seen as particularly vulnerable as its infrastructure has yet to recover from a devastating earthquake in 2010.
Low-lying Turks and Caicos is said to be at risk of a storm surge, with the possibility of destructive waves up to 6m (20ft) higher than usual.
Irma is a category five hurricane.
This is the highest possible level for a hurricane, and its winds are travelling at up to 185mph (290km/h). At least 14 people have already died in the region, and officials warn that the toll is likely to rise.
An estimated 1.2 million people have been affected by Irma and that could rise sharply to 26 million, the Red Cross says.
There are concerns that disease could spread rapidly in areas where drinking water and sanitation services have broken down.
The storm caused some damage to building and flooding as it approached Haiti, with rain and wind lashing the northern port city of Cap-Haitien.
“We’re asking all those living in areas at risk to leave their homes. If you don’t, you’ll be evacuated by force,” President Jovenel Moise said.
Preparations for the arrival of Irma are carrying on in the Turks and Caicos, which has a population of about 35,000. Its highest point is only 50m (163ft).
Governor John Freeman said: “We have decided to evacuate certain islands which were particularly low-lying and at threat. We have started to fill our shelters because a number of people who live in very low-lying areas are very vulnerable.”
Virginia Clerveaux, director of the Turks and Caicos Department of Disaster Management and Emergencies, told the BBC that even inland areas could be inundated by the storm surge.
“We are now trying to remind them [the people of the islands] that this is a category five, and in the history of the Turks and Caicos islands this is the largest storm we have ever been impacted or threatened by.”
Britain, France, and the Netherlands have sent ships, rescue teams and emergency supplies to their territories that have been hit by Hurricane Irma.
Aid efforts are being hampered by damage to local airports and harbours.
Irma is expected to hit Florida as a category four hurricane on Sunday, bringing storm surges and flooding.
“If you look at the size of this storm, it’s huge,” Florida Governor Rick Scott said on Thursday. “It’s wider than our entire state and could cause major and life-threatening impacts on both coasts – coast to coast.”
US President Donald Trump said: “I can say this: Florida is as well prepared as you can be for something like this. Now it’s just a question of what happens.”
Evacuations of tourists and residents of the Florida Keys, a resort archipelago, have begun.
Flights to and from airports in Florida are being suspended. Orlando’s international airport said commercial flights would stop from 17:00 local time on Saturday. (Courtesy BBC)