Eighteen people are missing after a boat carrying Cuban migrants sank off Florida due to Hurricane Ian, further underlining the human cost of the storm.

US border patrol said on Wednesday that it responded to a migrant landing in Stock Island, in the lower Florida Keys, Reuters said.

Four people swam to shore after their vessel sank, hours before the hurricane made landfall in Florida.

Three more people were rescued in the water and taken to hospital with heat exhaustion and dehydration symptoms, the US coast guard said.

A search and rescue effort led by the coast guard is under way. Authorities said on Thursday that they have rescued a total of nine people who were on the capsized boat, the US coast guard tweeted.

On Tuesday, seven people also from Cuba were taken into custody after making it to shore in Pompano Beach, Florida, just north of Fort Lauderdale, CBS News said.

Officials used social media to issue a warning about making the dangerous journey by sea, even after Hurricane Ian passes.

“Do not risk your life by attempting this journey at sea. Storm surge along with King tide can create treacherous sea conditions even after a storm passes,” they said.

Hurricane Ian battered Cuba, killing at least two people and leaving much of the island in total blackout. Millions were already facing daily power interruptions.

After making landfall in Florida, one of the most intense storms to make landfall in the US has continued to wreak havoc on hospitals and other essential infrastructure.

A hospital in Port Charlotte, Florida, an hour outside Venice, experienced serious flooding in its lower-level emergency room and had the roof of its intensive care unit torn off, the Associated Press reported.

Medical staff at HCA Florida Fawcett worked quickly on Wednesday to move its most vulnerable patients to other floors, as water flooded the hospital from above and below.

The hospital has four floors. Only two remained usable.

Dr Birgit Bodine, who was there when the roof came off, said patients had been mostly understanding amid damage from the storm but staff were worried about the potential influx of patients with storm-related injuries.

“The ambulances may be coming soon and we don’t know where to put them in the hospital at this point,” Bodine said, noting that patients were “doubled or tripled up” given the lack of space.

Bodine added: “For us, as much as everything is terrible and we’re exhausted … as long as our patients do OK and nobody ends up dying or having a bad outcome, that’s what matters.”