The official death toll from the partial collapse of a high-rise condominium complex near Miami, US, held at nine on Sunday, with more than 150 people still missing, as rescue teams picked through the rubble for a fourth day without finding further signs of life.

What caused nearly half the 12-story building to cave in on itself in the wee 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.

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.

A smoldering fire beneath the rubble that hindered the work of rescuers had abated by Sunday morning, officials said.

Only remains have been recovered since the early hours of the disaster.

Some residents remain in Champlain Towers North, a sister building where only a voluntary evacuation order has been issued. An inspector did not find any immediately obvious problems with the north tower.

Officials said on Saturday that Miami-Dade County would audit all buildings more than 40 years old within the next 30 days to ensure their safety.

Surfside officials have released documents including the engineer’s report from 2018, which cited major structural damage beneath the building‘s pool deck and “concrete deterioration” in the underground parking garage.

The report was produced for the Champlain Towers South condominium board in preparation for a major repair project set for this year.

The report estimated it would cost $9.1 million to make the recommended repairs. Work had started on replacing the roof, but the pandemic slowed the project, she said.

Satellite data from the 1990s showed the building was sinking 1 to 3 millimeters per year, while surrounding buildings were stable, according to Florida International University professor Shimon Wdowinski.