US President Donald Trump voiced serious concern Thursday as Hurricane Irma cut a path of devastation across the Caribbean toward Florida.

"We are very concerned, we are working very hard" Trump said of the storm, which has transformed a string of tropical island paradises into scenes of ruin.

"We think we are as well prepared as we could possibly be," he said in the Oval Office.

"Florida is as well prepared as you can be for something like this, now it's just a question of what happens."

"We are with the people of Florida."