Cadaver dogs arrive at Iowa building collapse in race against time to find survivors

An elite task force with dogs trained to smell death is combing through a partially collapsed building in eastern Iowa as three people remain missing.

Iowa Task Force 1, a Cedar Rapids-based urban search and rescue team trained and equipped by the Federal Emergency Management Agency, arrived in the city of Davenport on Thursday, four days after a section of a six-story residential building collapsed. The team brought "live and cadaver canines," or dogs trained to pick up the scent of humans both alive and dead, according to a press release from the city government.

The task force met with city officials and the Davenport Fire Department before entering the structure with the dogs. The team is now working to "re-verify and mark all rooms with standard FEMA markings," the city said.

It's become a race against time to find and rescue any survivors since part of The Davenport collapsed for unknown reasons on Sunday afternoon. The building, located in the heart of downtown Davenport, houses commercial space at the street level and residential units in the floors above. More than a dozen people evacuated at the time of the collapse, while eight others and several pets were rescued in the 24 hours that followed.

On Monday, officials said there was no credible information that anyone was missing and the city would move forward with plans to begin demolishing the remaining structure the next day. But that night, rescuers found a ninth person alive inside and pulled her out of a fourth-story window. It was unclear how the woman was not found earlier by crews using thermal imaging, drones and dogs. The development prompted protests from members of the community calling for the demolition to be delayed.

On Tuesday, the city's demolition plans were put on hold as officials announced that five residents were still unaccounted for, including two -- 42-year-old Branden Colvin and 51-year-old Ryan Hitchcock -- who may be inside. Crews rescued several more animals from inside the structure that afternoon but no human activity was detected, according to officials.

Then, on Thursday, officials announced that only three residents remain missing -- Colvin, Hitchcock and 60-year-old Daniel Prien. All three lived in apartments located in the collapse zone and were believed to be home at the time. However, officials have struggled to locate family for Prien to confirm his whereabouts. Officials called it a "recovery situation" for Colvin and Hitchcock, noting that they're likely inside the structure in an area that's "not sustainable for life."

Officials have warned that the structure is unstable and continues to degrade. Crews are working with structural engineers on how to best search the building while avoiding the pile of debris, which is currently contributing to the stability and its "removal could jeopardize or accelerate the inevitable collapse of the building," according to the city.

ABC News' Jianna Cousin, Laryssa Demkiw, Alexandra Faul, Andy Fies, Jessica Gorman, Ahmad Hemingway, Alex Perez, Darren Reynolds and Emily Shapiro contributed to this report.