MIAMI (NYTIMES, REUTERS, AFP) - Rescue workers frantically scoured the rubble of a collapsed apartment block in a Miami suburb for signs of life on Friday (June 25), as the death toll from the disaster crept up and more than 150 people remained unaccounted for.

At least four people are now known to have died in the collapse of the Florida apartment block, the county’s mayor said as search operations entered a second day.

“Tragically, I woke up to learn that three bodies had been pulled from the rubble last night,” Miami-Dade County Mayor Daniella Levine Cava said on ABC’s Good Morning America. “It does bring our count to four, of those who have lost their lives in this tragedy."

The number of people unaccounted for has risen to 159, the Mayor told a news conference.

“We do have 120 people now accounted for, which is very, very good news. But our unaccounted for number has gone up to 159,” she said.

The authorities have stressed that it is still unclear how many people were inside the building when it pancaked in the early hours of Thursday.

US 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 authorises the Department of Homeland Security, Federal Emergency Management Agency (Fema), to coordinate 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 condominium in Surfside, a barrier island town across Biscayne Bay from the city of Miami, crumbled to the ground, the 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 1.30am (1.30pm Singapore time), 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-storey tower was undergoing roof construction and other repairs.

As families of the missing grew increasingly desperate for answers, search crews were trying to tunnel to different floors and find spaces where survivors might be, setting up cameras and sonar devices to detect any signs of life.

At each turn, they were confronted by danger as pieces of the wreckage fell and a fire broke out.

"This process is slow and methodical," Mr Ray Jadallah, a Miami-Dade Fire Rescue assistant fire chief, said at a Thursday afternoon news conference. "Any time we started breaching parts of the structure, we get rubble falling on us."

Survivors have described the collapse as being "hit like a missile", the authorities said.

Ms Erika Benitez, a public information officer for Miami-Dade Fire Rescue, said that officials hoped the noises they heard in the wreckage could be signs of life.

"This is what you'll typically hear when doing search and rescue," she said. "People who are trapped, and they may be too tired to speak. Falling asleep could also be a coping mechanism."

Florida Governor Ron DeSantis said after touring the wreckage that search and rescue teams had "made contact" with some people and still hoped to identify survivors caught in the dusty jumble of concrete and steel.

The collapse transformed the picturesque town of Surfside, population 5,600, with its art deco hotels and mid-rise residential buildings, into a dazed scene of disaster and grief.

Families flocked to a community centre for news about missing loved ones. Survivors recalled being jolted awake at about 1.30am to fire alarms, falling debris and the feeling of the ground trembling.

Rescue teams, some with dogs, picked through an unstable mountain of wreckage on Thursday amid concerns about the stability of the remaining part of the condo building.

At one point, clouds of dust and smoke swirled through the scene as a fire broke out at the site, according to a Miami-Dade Police spokesman.

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 Local 10.

Ms Raysa Rodriguez, 59, who lives in the part of the building that remained standing, said she was awakened by what she thought was an earthquake. She then escaped down an emergency stairwell and off a second-floor balcony onto a rescue ladder.

"I lost a lot of friends," said Ms Rodriguez, who has owned a unit in the building since 2003. "They are not going to be able to find those people."

The area has a robust Jewish community and long-time ties to South America from decades past when families kept beach apartments there, and many Jewish and South American residents were reported to be among the missing.

Not far from the collapsed building is a stretch of beloved businesses that include an Argentine bakery, a Venezuelan bakery and a Cuban restaurant. Farther north are the ritzier municipalities of Sunny Isles Beach and Bal Harbour.

Surfside Mayor Charles Burkett said it was unclear how stable the rest of the building was. He said 15 families were being relocated to hotels.

"We don't know if the rest of that building is going to come down," he said.

He said the scale of the collapse was overwhelming.

"There's not a lot that little Surfside can do but ring the alarm bell," Mr Burkett said at a news briefing on Thursday afternoon.

Associate Professor Fiorella Terenzi from the Florida International University who lives in a neighbouring building, Champlain Towers East, said she was woken up by a loud noise.

The sound "was like a big thump all of a sudden", she said. At first she thought it was thunder but then started to hear sirens. When she left the building, dust was everywhere.

"I could see that half of the building of the Champlain Towers South was collapsed like a sandwich," said Prof Terenzi, 59, who has lived in the east tower since 2000. "It really was a shocking view."

Prof Terenzi said she had seen heavy equipment on the roof of the south tower for the past two weeks.

Joining the families searching for missing loved ones was Paraguay’s first lady Silvana López Moreira, who travelled to Florida because her sister, brother-in-law and their children were unaccounted for. The first lady’s family owned a condo in the building.

The South American country’s foreign ministry said Ms Sophia López Moreira, her husband Luis Pettengill and her three young children were among six Paraguayans missing since Thursday after the collapse of the building.

“She travelled to Miami and is there accompanying her parents,” a spokesman for her office told Reuters. The spokesman declined to comment further on the situation.