The Bahamian prime minister has said the islands are in their “hour of darkness” as conditions “rapidly” deteriorate six days after Hurricane Dorian ripped through.
Tens of thousands of people are homeless and it is estimated that around $3bn (£2.4bn) in insured property has been damaged in the Caribbean.
The official number of dead – 43 – is expected to rise as the situation becomes clearer.
Prime Minister Hubert Minnis said: “We acknowledge that there are many missing and that the number of deaths is expected to significantly increase.
“This is one of the stark realities we are facing in this hour of darkness.”
The US Coast Guard says it has rescued 290 people in the Bahamas.
Cruise ships have also been helping to deliver supplies, health workers and emergency crews to the islands, also ferrying survivors to the US. About 1,100 people who had been evacuated by ship arrived in Florida, weary but safe.
Aid is arriving from a number of countries – including Britain, which has sent Royal Navy medics and pledged £1.5m in aid.
The Royal Navy has so far provided emergency shelter and hygiene kits for hundreds of people, more than 8,000 bottles of water and hundreds of days worth of food.
Herve Verhoosel, spokesman for the UN’s World Food Programme, said the needs “remain enormous”.
He added: “Evacuations are slowly taking place by ferry, as hundreds of residents reportedly flee daily.”
Red Cross spokeswoman Jennifer Eli said: “Our relief operation is growing, but we are also facing serious challenges in terms of delivering aid.
“Even search-and-rescue choppers haven’t been able to reach some people because there’s no place to land. These challenges are affecting everyone.”
On Friday Dorian, which hit the Bahamas as a category five storm but is now a category two, pounded parts of North Carolina. There were no reports of serious injury there but about 200 people are in shelters and almost 60,000 homes without electricity.
Dorian is now hitting the Atlantic coast of Canada, and has left about 500,000 people without power. Heavy winds and rain toppled a construction crane in Halifax, and authorities warned people to secure heavy items that could be swept up and cause damage.
The National Hurricane Center said the post-tropical cyclone was about 60 miles (97km) south of the Magdalen Islands with maximum sustained winds of 90 mph (145 kph), at 3am Sunday (UK time).
In the south of Halifax, a roof was ripped off an apartment building which was under construction. Firefighter Jeff Paris said buildings were being evacuated.
When it hits Nova Scotia later on Saturday, it is expected to weaken, bringing winds of 85mph and up to seven inches of rain.
It made landfall 15 miles (24km) south of Halifax, Nova Scotia on Saturday evening.
Hurricanes are somewhat rare in Canada because once the storm reaches the colder waters, they lose their main source of energy.