Rescuers continued to search through the rubble of a collapsed Miami condo on Saturday as it emerged that a 2018 report had warned the building needed urgent repairs.

Part of a 12-story apartment block in the Surfside suburb caved in suddenly on Thursday as residents slept, killing at least five people.

As many as 156 people are unaccounted for, fueling fears of a much higher death toll. 

Miami-Dade Mayor Daniella Levine Cava said crews also discovered other unspecified human remains.

What about the rescue efforts?

Rescue teams are using sniffer dogs, camera, and sonar equipment in the race to find survivors.

They used heavy machinery to sift through the debris, including two large cranes.

Teams from Mexico and Israel have arrived in Miami to help with the efforts of the local crews.

Crews had to fight flames on Saturday in the debris, hampering their search

New information emerges about the building

Officials have repeatedly stressed that the cause of the building's collapse remains unknown.

But a report published late on Friday showed that a consultant for a major engineering firm had warned three years ago that the building had shown evidence of "major structural damage."

The recommendations had formed the basis of planned renovation work that was set to get underway soon.

Champlain Towers was built in 1981 and local regulations state that changes were needed to the 40-year old building in order to obtain a new safety certificate.

Vice Mayor Tina Paul called the structural issue identified in the report "very alarming" in an email on Saturday morning.

What did the report say?

Engineer Frank Morabito wrote in the report that the waterproofing installed below the pool deck had failed due to a major error in design.

"The failed waterproofing is causing major structural damage to the concrete structural slab below these areas," he wrote.

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

Morabito gave no indication in his report that the structure was at risk of collapse.

He pointed out that the repairs would be aimed at "maintaining the structural integrity" of the building and its 136 units.

His findings had been submitted to local Miami authorities back in April ahead of the planned work.

What happened to the building?

A large section of the oceanfront Champlain Towers in Surfside crumbled to the ground at around 1 a.m. local time on Thursday.

CCTV footage showed an entire side of the building suddenly folding in two sections, spitting out clouds of dust.

Officials said roughly 80 units of the apartment block were occupied at the time of the incident.

Eyewitnesses described hearing what sounded like thunder when the collapse occurred.

Families angry over 'slow' rescue operation

Some families, urgently waiting for news of loved ones, have criticized the slow pace of the rescue operation.

"Not enough is being done," said Mike Salberg, who came from New York after the accident. "I want answers."

Salberg said that five of his family members, including his parents, are unaccounted for.

"My friend's mom is there (under the rubble)," a man who identified himself only as Mark said.

"We want to be hopeful but also we have to be realistic. The next step is being there for the families and know why this happened."

kmm,jf/nm (AP, AFP, Reuters)