Rescue workers are pinning their hopes on finding a "miracle" survivor in voids underneath the rubble of a Florida apartment building which collapsed five days ago.
Miami-Dade Fire Rescue Chief Andy Alvarez said a "frantic effort" was underway to reach any air pockets where people could have survived.
No one has been pulled alive from the site since Thursday, when the building in Surfside, north of Miami, collapsed.
At least 11 people have died.
More than 150 people are still missing, and officials say they are refusing to give up hope.
"We're going to continue and work ceaselessly to exhaust every possible option in our search," Miami-Dade County Mayor Daniella Levine Cava told media. "The search-and-rescue operation continues."
Rescuers are searching through the rubble in sweltering heat and high humidity. Initial efforts were slowed by several fires in the debris.
US emergency crews have now been joined by teams from Israel and Mexico to help in the painstaking, round-the-clock operation. Machinery has moved large slabs, and a trench measuring 125ft (38m) long and 40ft deep has been built to help them reveal any potential air pockets in the wreckage of the 12-storey building.
Surfside Mayor Charles Burkett previously described how the building had "pancaked", with spaces that were 10ft or more reduced to "just feet".
Mr Alvarez told ABC News that a number of voids had already been found. He said the huge cranes which had been brought to the site were now helping them "to laminate this building, almost like an onion, so that we can get inside and, again, find those voids that we know might possibly be there and rescue those people".
Sniffer dogs and listening devices are also being used to search for signs of life. But as yet, they have not revealed any survivors.
"We hear falling debris, twisting metal," Maggie Castro, a paramedic with the Miami-Dade county fire department, told AFP news agency. "We have not heard human sounds."
Who are the victims?
Eight of the 11 victims have been named by officials so far: Gladys Lozano, 79, and her husband Antonio, 83; Stacie Fang, 54; Manuel LaFont, also 54; Leon Oliwkowicz, 80; Christina Beatriz Elvira, 74; Luis Andres Bermudez, 26, and his mother Anna Ortiz, 46.
Ms Fang's son, 15, was pulled alive from the rubble.
Miami Dade Police director Alfredo Ramirez III said on Monday that investigators would use rapid DNA tests when possible to identify deceased victims found amid the ruins.
What happened to the building?
The Champlain Towers South building contained 136 apartments and 55 of them collapsed early on Thursday, leaving piles of debris.
Resident Barry Cohen, who was in bed in a section of the building that survived when the collapse happened, said it sounded "like thunder".
"When we opened the door, there was no building there, it was just a pile of rubble," he said.
Federal investigators are already on site and working to find the cause of the collapse and ensure evidence is preserved.
At a press conference on Monday, Florida Governor Ron DeSantis said the investigation, conducted by National Institute of Standards and Technology (NIST), would be thorough and "will not happen in a day or two".
"This will take a long time. That is the time horizon they work on," he said.
White House Press Secretary Jen Psaki said that there are dozens of federal officials at the scene - including building science experts, structural engineers, geotechnical experts, the FBI and Army Corp of Engineers.
She added that President Joe Biden "does believe that there should be an investigation", but did not specify which agency should lead a federal probe.
Under Florida law, buildings must be inspected every 40 years, and as the Champlain Towers complex has stood since 1980, inspectors were about to start its recertification process.
But a number of reports on the building had been done ahead of this inspection.
An engineer's report from 2018, which was made public on Saturday, highlighted "a major error" in the original design of the 12-storey seafront building. It said the fault prevented water draining away from the base of the building.
The report flagged "major structural damage" to the concrete platform beneath the swimming pool deck. It also referred to "abundant cracking… of columns, beams and walls" in the garage.
The report did not suggest the 40-year-old building was at any imminent risk of collapse but its author, engineer Frank Morabito, urged that the concrete repairs be carried out in "a timely fashion".
Meanwhile, a study published last year by researchers at Florida International University found that the building had been sinking at a rate of two millimetres per year in the 1990s, which may have affected it structurally.
But the author has cautioned that the study was just a snapshot in time. The building was constructed on reclaimed wetland, which experts say is always of concern as the land underneath can compact over time, leading to shifts.
On the sinking, the author of the study, Prof Shimon Wdowinski, told the Miami Herald newspaper: "We've seen much higher than that, but it stood out because most of the area was stable and showed no subsidence."
Prof Wdowinski reiterated the research was not meant to suggest certainty about the latest incident.
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