By Brendan O'Brien

Two of five people still missing after the partial collapse of an Iowa apartment building this weekend were likely inside at the time, officials said on Tuesday, but the structure is too unstable to immediately resume a search for them.

Experts were evaluating the structural integrity of the part of the building that remained standing after suspending a search through the rubble out of concern for the safety of rescue workers, said James Morris, fire marshal for Davenport, a small city on the Mississippi River, just west of Illinois.

"The building is unstable and continues to worsen as time progresses," he said at a news conference. "We are very sympathetic to the possibility that there are two people still left inside."

Officials declined to comment on why only two of the five were believed to have been inside at the time of collapse, and did not disclose the possible whereabouts of the other three.

"This is an unthinkable situation, especially for the families involved and impacted," Davenport Mayor Mike Matson said.

One of the two people thought to be inside the building was identified as Ryan Hitchcock by Amy Anderson, a relative of his.

Anderson said during the briefing that she understood why the search for Hitchcock had been suspended.

He "probably has not survived. I don't discount that he could be trapped under there miraculously ... but we don't want to see anyone else lose their lives or anyone else be injured," she said.

On Sunday afternoon, immediately after the collapse, rescue teams were able to pull seven people to safety from multiple floors of the building, some by fire ladder.

With the help of six rescue dogs, first responders pulled an eighth person from the rubble on Monday. Another dozen people walked out on their own, officials said. No fatalities have been confirmed.

The collapse involved one side of the center section of the structure that contained 84 apartments and businesses. When that section pancaked, support beams were left dangling from upper floors and the interiors of some apartments were exposed. In one case, the inside of a closet neatly lined with clothing on hangers was visible from the street.

City officials said the building had been inspected several times in recent years, both for complaints and routine inspections, but declined to speculate on a cause.

(Reporting by Brendan O'Brien in Chicago; Editing by Mark Porter)