Responders discovered a “large natural gas leak, with water leaking from all floors” for the six-story building, even if the cause of the collapse is yet unknown.

After a six-story apartment building in Davenport, Iowa partially fell on Sunday, local authorities are focusing their efforts on “the whole purpose of trying to find people and trying to get them out.”

At a press conference held Sunday evening, hours after the building known as The Davenport fell in the afternoon, Mayor Mike Matson and city officials provided citizens with updates.

Crews were called to the scene around 4:55 p.m. local time when a portion of the building’s back broke away from the remainder, however the reason for the collapse is yet unknown.

According to the Quad-City Times, Matson and Davenport Fire Chief Mike Carlsten stated during a press conference that the building’s integrity was a worry. The first responders discovered a “large natural gas leak, with water leaking from all floors of the structure.”

According to Carlsten, crews first assisted in the rescue of seven people and helped more than a dozen more leave. Since then, other agencies have joined the effort to provide additional “expertise” and “manpower.”

CNN quotes Carlsten as saying that a second person was pulled from the building overnight. At yet another news conference on Monday, he said, “The building is structurally unsound and is posing a risk to responders.”

The building’s structural stability and the search for missing people remain some of our current worries, Carlsten said on Sunday.

The crews will work into the night. In fact, workers have just recently begun to re-enter the structure for the secondary search and to begin the effort to rescue the pile of wreckage at the ground level. We’ll keep doing that till this operation is finished.

The building’s owner had authorization to perform “exterior wall repairs,” according to Richard Oswald, the city’s neighborhood services director, who spoke at the press conference on Sunday.

Images taken at the scene show a portion of the building fully open, with the interiors of closets and other rooms of units being clearly visible as water dripped down from the top of the building.

From outside the building, rescuers could see the “glows” of their flashlights as they searched each apartment for trapped people and animals.

Local networks have been informed of residents’ worries and what they observed. Tadd Machovec, a building cleaner, remembers “a lot of screams and a lot of cries” when a portion of the structure collapsed.

According to him, “that did not last,” he told WQAD. “After 2 or 3 minutes, the neighborhood fell silent. I’m crossing my fingers and hoping that the screams I heard when the building collapsed were not from anyone inside.

I hope they bring my dog out and that she’ll come back out to me, said Victoria McClain, a resident, who remembered seeing dust and debris. I live in her world. She is all I have.

KWQC interviewed former resident Andrew Sommer, who said: “I live in the building right next to it and we heard just like a large crash and then shortly after we went outside we saw the whole section of the building gone.”