Rescue workers are frantically scouring the rubble of a collapsed apartment block in a Miami suburb for signs of life as the death toll from the disaster creeps up, with more than 150 people still unaccounted for.
Miami-Dade Mayor Daniella Levine Cava told the media that three more bodies were pulled from the wreckage overnight, raising the overall death toll to four after another person died on Thursday.
US President Joe Biden had ealrier approved an emergency declaration in the state of Florida and ordered federal assistance to supplement state and local response efforts.
"The President's action authorises the Department of Homeland Security, Federal Emergency Management Agency (FEMA), to co-ordinate all disaster relief efforts," the White House said on 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 apartment building in Surfside, a barrier island town across Biscayne Bay from the city of Miami, had crumbled to the ground, authorities said.
What caused the 40-year-old high-rise to tumble into a heap in a matter of seconds was not immediately known, although local officials said the 12-storey tower was undergoing roof construction and other repairs.
Cava told reporters on Thursday 159 people remain unaccounted for, although some may not have been in the building at the time.
Another 102 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 pulled two individuals from the rubble. One of them was dead.
Officials said the complex, built in 1981, was going through a re-certification 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 re-certification process and the adjacent building construction.
Australia's Department of Foreign Affairs and Trade said it was aware of reports citizens may have been caught up in the disaster.
"The Australian embassy in Washington is closely monitoring developments and making urgent enquiries to determine if any Australians were affected," it said.
Veronica Zaragovia, a reporter for local radio station WLRN, told the ABC people from all over the world had made a home at Champlain Towers South.
"There are people from many countries, including Venezuela, Peru, Puerto Rico, the US - and Australia," she said.
"South Florida and Miami-Dade County is very international and so yesterday I had spoken to a man who lives in Surfside from Australia and he was actually at the beach and he was waiting to hear from two friends from Australia.
"And I saw him later in the evening and he had ... (he) was still waiting to hear about their wellbeing."
Australian Associated Press