On Monday, hundreds of would-be rescuers laboriously dug through a mountain of crushed concrete, mangled steel, and smashed belongings as officials vowed to continue the desperate search for survivors of last week’s condominium collapse.

The effort, according to state officials, was the largest non-hurricane search-and-rescue mission in Florida history. But, for the fifth day in a row, the dangerous work produced little reason for optimism: two more bodies were discovered among the still-smoking rubble, bringing the total number of confirmed dead to 11; 150 people remained missing.

With the grim reality sinking in, loved ones of those still missing were shuttled to the oceanfront debris pile that was once Champlain Towers South to stand vigil, pay respects, and see for themselves what is being done to find signs of life. They have witnessed harrowing scenes while there: One of the rescuers fell 25 feet. An official stated that the firefighter refused medical attention and continued to work.

Officials said that, despite the dangers to those working on the vast and treacherous site, the search would continue, with no timetable for transitioning from rescue to recovery. They also stated that they were being open and honest with family members about the dwindling chances of survival with each passing day.

Federal investigators from the National Institute of Standards and Technology (NIST) were among those looking for clues on Monday, though no immediate answers are expected.

Authorities had good reason to make an exception: the Champlain Towers could be the deadliest accidental building collapse in American history. And the investigators’ final findings could have far-reaching implications not only in Florida, but also elsewhere.

However, because there were few solid theories as to why the tower collapsed, it was unclear what those fixes might be.

On Monday, eight rescue teams from across Florida, as well as Israel and Mexico’s international rescue team, Topos Azteca, participated in the search. Out-of-state help also poured in, with Virginia sending an engineer from Fairfax County to assess which areas of the rubble were safe, according to Jeff Lewis, chief of the Fairfax County Fire Department.

Torches, specially trained dogs, and seismic acoustic sensors that resemble coffee cans and can hear tapping through rubble from dozens of feet away are among the tools used in urban search and rescue.

The task at hand is extremely delicate. According to Gregg Favre, executive director of the St. Louis regional response system, first responders are essentially constructing a makeshift mineshaft in the hopes of reaching people who have been insulated in a void amid the debris.

According to Ken Keen, a retired three-star Army general who led the military’s relief efforts following the 2010 earthquake that devastated Haiti, the cruel randomness of the collapse will put strains not only on the families of the missing, but also on rescue teams working in heat, dust, and jagged fragments looking for miracles.

Despite the fact that rescuers have not found survivors since the collapse’s early hours, they have discovered items that remind them of who they are looking for: a football. A plush animal. T-shirt for a bar mitzvah.

Rescuers have gathered the belongings to be left at a memorial set up a block away. The memorial has become a place for those digging through the rubble to leave mementos — possibly once prized by their owners, but now treasured as the last traces of people who have vanished.

Eyal Golan was among those who took a bus from the Grand Beach Hotel to the rubble pile where his friend, Estelle Hedaya, who is still missing, once lived.

Golan tilted his head up, counting the units to Hedaya’s floor, and saw what he assumed was her apartment, which had been ripped in half by the collapse. He said the balcony and living room were fine, but the den and bedroom had been ripped apart — and the master bedroom had been destroyed. People around him dealt with the tragic scene in their own unique ways. Some people prayed quietly. Some people were staring at the structure. Others yelled the names of their missing loved ones into the midst of the devastation.