According to the official death toll from the partial collapse of a high-rise condominium complex near Miami on Sunday, nine people were reported dead and more than 150 people still missing.

Iran PressAmerica: Reuters reported that rescue teams picked through the rubble for a fourth day without detecting further signs of life.

What caused nearly half the 12-story, 156-unit building to cave in in the early hours of Thursday as residents slept has yet to be determined, but a 2018 engineer's inspection report found major structural deterioration in the parking garage beneath the 40-year-old tower.

Officials in Surfside, the shore town near Miami where the building stood along the beach, said hope remained that rescuers would yet discover survivors in air pockets that may have formed in the pancaked debris.

Even so, Fire Chief Alan Cominsky said on Sunday that crews had yet to find such voids in the rubble or signs of anyone alive since early in the tragedy, when faint sounds were detected.

"It's an extremely difficult situation," Cominsky said. "Our rescue teams are nonstop, doing all that we can, searching every area, every bit of hope, to see if we can find a live victim."

Two large cranes and two backhoes on Sunday joined in the debris-removal efforts that had previously been conducted essentially by hand by teams also using rescue dogs, sonar, drones and infrared scanners as they gingerly tunneled through the ruins.

Miami-Dade Mayor Daniella Levine Cava said six to eight squads of rescuers were working on the multi-story pile of shattered concrete and twisted metal laying next to the portion of the Champlain Towers South condo that remained standing.

"Hundreds of team members are on standby to rotate as we need a fresh start," Levine Cava said at a briefing in which she announced the death toll had risen to nine, with the number of individuals still unaccounted for standing at 152.

The mayor later said those figures would remain "extremely fluid."

Given the scores of those still missing, the disaster may end up to be one of the deadliest non-deliberate structural failures in U.S. history.

By comparison, 98 people perished when the roof of the Knickerbocker Theatre in Washington, D.C., gave way from the weight of snow during a silent movie screening in January 1922. Two interior walkways collapsed into the lobby of the Hyatt Regency hotel in Kansas City, Missouri, during a party in July 1981, killing 114 individuals.

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Death toll climbs to five, dozens missing at collapsed Florida building