(CNN) — Two people may still be inside a six-story apartment building that partially collapsed Sunday afternoon in Iowa, Davenport's mayor said midday Tuesday, while three others remain missing as rescue efforts continue at the structurally precarious tower.

The revelation followed the rescue Monday afternoon of a ninth survivor from the rubble, Mayor Mike Matson confirmed less than a day after city officials announced that "demolition is expected to begin in the morning" at the site after rescue efforts "transitioned to a recovery operation."

That plan is now apparently on hold. Even so, the building remains dangerous, and only the first responders are allowed to enter, as stressed on Tuesday by the municipal authorities.

"This is an active incident that is very rapid and constantly evolving," Matson said Tuesday during a news conference, adding that he doesn't know why the ninth survivor, Lisa Brooks, wasn't found sooner.

"But please understand, me and the city (are) committed to finding out why," the mayor said.

The city is "continually evaluating the date of the demolition," the city said in an update Tuesday.

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"The demolition is a multi-phase process that includes permitting and staging equipment that will begin today," the city said. "The timing of the physical demolition of the property is still being evaluated. The building remains structurally unsafe and in imminent danger of collapse."

Officials acknowledged Monday night that "there are missing persons who were residents of the property" and Davenport police continue to work "to try to communicate with them."

With the building's exterior wall peeling off, exposing a bathtub and clothes still hanging in a closet, images of its partial collapse evoked memories of the 2021 condominium building collapse in Surfside, Florida, in which 98 people died. Last month, in New York City, a parking lot with property violations collapsed, killing one person and injuring at least five.

• Person rescued as search continues for survivors at partially collapsed apartment building in Davenport, Iowa

The cause of the collapse in Davenport has not yet been determined, but the building's owner had current permits for exterior wall repairs, authorities said. Now, that owner has been notified with a demolition order, Davenport officials said Monday afternoon.

"The building remains in imminent danger of collapse and conditions at the site continue to worsen," the city said in an update Monday night.

The "need to demolish this building stems specifically from our desire to maintain as much safety as possible for the surrounding areas," said Rich Oswald, director of City Development and Neighborhood Services.

City officials did not immediately respond to CNN's requests for more details about the missing, the demolition plan and the building.

"Take it out"

Brooks had been missing since part of the building broke off and collapsed Sunday, the Quad-City Times reported. She called her daughter from the fourth floor of the building Monday, and family members rushed to alert firefighters and police officers at the scene of her location.

Firefighters raised a bucket ladder to rescue Brooks, who waved through a window. The crowd cheered and chanted, "Get her out," the newspaper reported.

Bystanders look at the remains of a partially collapsed apartment building Monday in Davenport, Iowa.
Scott Olson/Getty Images

Eight other people were previously rescued from the collapsed building and more than a dozen managed to evacuate on their own, according to city authorities. No deaths have been reported.

"After extensive rescue operations, no viable signs of life have been confirmed," the city said in a news release Monday night. "After multiple rescue evolutions over the course of the 24 hours since the incident, teams were unable to find any victims who needed to be rescued."

Protesters gathered Monday night after news of the planned demolition, saying some residents could still be trapped, the Quad-City Times reported. Some carried banners reading, "Who's in the rubble?" and "Find them first!"

Engineers have been studying how to carry out the demolition in Davenport.

"In the opinion of the structural engineer, the pile of debris currently contributes to the stability of the building and its removal could jeopardize or accelerate the inevitable collapse of the building," city officials said Monday night.

The damage occurred when the rear of the apartment building detached from the rest of the structure, Davenport Fire Chief Mike Carlsten said. Sunday's collapse triggered a major natural gas and water leak that forced emergency crews to halt their search and rescue efforts until utilities could be secured, he said.

Residents will not be allowed to re-enter the building for security reasons, according to authorities.

The collapse was like "a bomb"

The collapse destroyed entire rooms with residents' most prized possessions and left some without a place to live, they said.

Army veteran Fred Voorhis lost all memories of his 21 years of military service, as well as several essential medications, he told CNN affiliate KGAN. Voorhis was sleeping when the collapse occurred.

"I opened the door to my apartment and there was sunlight. It was supposed to be a hallway," Voorhis told the affiliate. With his house in ruins, he said he has no idea where he's going to live.

"There is no alternative plan," he said.

Residents of the partially collapsed building will not be able to collect their belongings again, according to authorities.
Nikos Frazier/Quad City Times/AP

Paul Stephenson, who was visiting a friend who lived in the building at the time of the collapse, told CNN affiliate KWQC that he was able to help his friend escape the building but hasn't seen him since emergency crews escorted residents Sunday night.

The moment of the collapse was "like a bomb" that echoed throughout the building, he said.

"It was very dark. I just knew how to get my bearings," Stephenson said, describing how he helped guide his friend from the rubble, but had to leave his phone in the chaos.

"I'm still looking for my friend. " But I know he's safe because I pulled him out."

He said he knows others, however, who are nervous waiting for news of their loved ones.

Davenport Mayor Mike Matson acknowledged that the collapse is "devastating for the residents of this building and also for our community."

"My prayers are with the families of those still missing and for a speedy recovery for those who were injured," he said.

CNN's Elizabeth Wolfe, Kelly McCleary and Taliah Miller contributed to this report.

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