U.S. President Joe Biden has offered his administration's support following the building collapse in Florida.

Biden said federal resources were ready for deployment, having already approved an emergency declaration overnight and ordering federal assistance to supplement state and local response.

"We are ready to move for the federal resources immediately," he said.

"To the people of Florida — whatever help you want, the federal government can provide"

Earlier, Miami-Dade County Mayor Daniella Levine Cava said at least four people have been confirmed dead, and the number of people unaccounted for has risen to 159 following the collapse of a condo building.

"We do have 120 people now accounted for, which is very, very good news," the mayor told a press conference.

The reason that caused the 40-year-old high-rise to collapse is still under investigation.