U.S. officials say there are still 159 people unaccounted for as the death toll rises to four after the partial collapse of a beachside building in Florida.

Rescue workers frantically scoured the rubble of a collapsed apartment block in a Miami suburb for signs of life Friday, after the oceanfront condo dramatically crumpled in a matter of seconds.

Miami-Dade Mayor Daniella Levine Cava said that the number of people missing had risen from the initial 99, and that three more bodies were pulled from the wreckage overnight. Another person was reported to have died Thursday.

U.S. President Joe Biden approved an emergency declaration in the state of Florida and ordered federal assistance to supplement state and local response efforts.

"The President's action authorizes the Department of Homeland Security, Federal Emergency Management Agency (FEMA), to coordinate all disaster relief efforts," the White House said Friday.

On Thursday, search teams detected sounds of banging and other noises but no voices coming from the mounds of debris.

Early that morning, a large section of the Champlain Towers South condominium in Surfside, a barrier island town across Biscayne Bay from the city of Miami, crumbled to the ground, authorities said.

Footage captured by a security camera nearby showed an entire side of the building suddenly folding in two sections, one after the other, at about 1:30 a.m. (5:30 a.m. GMT), throwing up clouds of dust.

What caused the 40-year-old high-rise to cave in was not immediately known, although local officials said the 12-story tower was undergoing roof construction and other repairs.

Cava told reporters Thursday that 99 people remained unaccounted for, although some may not have been in the building at the time of the disaster.

Another 110 individuals whose whereabouts were initially unknown have since been located and "declared safe," she said.

A fire official said earlier that 35 people were evacuated from the portion of the high-rise left standing, and response teams using trained dogs and drones in the search pulled two individuals from the rubble. One of them was dead.

Officials said the complex, built in 1981, was going through a recertification process requiring repairs, with another building under construction on an adjacent site.

The Champlain Towers South had more than 130 units, about 80 of which were occupied. It had been subject to various inspections recently due to the recertification process and the adjacent building construction, Surfside Commissioner Charles Kesl told news channel Local 10.