• In the middle of the night Thursday, a condominium tower near Miami partially collapsed, leaving four dead and 159 people missing.
• Nearly three years before, an engineer warned that the building's failed waterproofing of its pool deck was causing "major structural damage," according to filings.
• The report did not warn of any imminent danger, and it's still unknown what caused the building's collapse.

Nearly three years before a Florida condo tower collapsed, an engineer warned that the building's failed waterproofing of its pool deck was causing "major structural damage," according to filings.

Champlain Towers South, the 12-story condominium tower in Surfside, Florida, partially collapsed in the middle of the night on Thursday. The death toll has risen to four people, while 159 remain missing.

Officials said Saturday at a news conference that fire and smoke coming from deep inside the remains of the tower is slowing down the search. As rescue efforts continue, the city of Surfside has released a number of documents about the building.

Among the filings released by Surfside authorities late Friday is a 2018 field survey report from Morabito Consultants, which found that the concrete structural slab underneath the building's pool needed repairs.

"Failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially," the report said.

The firm recommended replacing the damaged slabs. It also found "abundant cracking and spalling" in the concrete columns, beams and walls of the parking garage. The tower was built in 1981.

CNBC has reached out to Morabito Consultants for comment.

The report did not warn of any imminent danger, and it's still unknown what caused the building's collapse. Surfside Mayor Charles Burkett told CNN that he had not seen the 2018 structural field survey report but said it's "unclear right now exactly what was going on in that building." According to The New York Times, the report helped shape plans for a multimillion dollar repair project that was set to start soon.

Burkett said during a news conference that he's working on a plan to relocate occupants of Champlain Towers North, which was built the same year. FEMA has agreed to pay for lodging. City officials are still gathering more information on Champlain Towers East, which is built in a different style and probably constructed at a different time.

Miami-Dade County Mayor Daniella Levine Cava said Saturday afternoon that she will order a 30-day audit of all residential properties that are more than five stories, at least 40 years old and have not completed the recertification process for buildings that are four decades old.

I’m directing the Department of Regulatory and Economic Resources to immediately begin a 30-day audit of all residential properties 5 stories+ at the recertification point – 40 years or older – that have not completed the process to identify and address any issues.

— Daniella Levine Cava (@MayorDaniella) June 26, 2021