Illinois Governor J.B. Pritzker announced that the death toll at the Edwardsville Amazon warehouse, about 25 miles east of St. Louis, has increased to at least six people during a press conference on Saturday evening.
Other officials at the press conference said that the focus of law enforcement has shifted to a search and recovery effort and noted that they don't expect that anyone can be surviving. The recovery is expected to take up to three or four more days.
The event was originally described by local emergency responders as a "mass casualty incident."
According to officials, 45 personnel members made it out of the building safely, and one individual was airlifted to a regional hospital for injuries sustained during the collapse.
James Whiteford, the Edwardsville Fire Department chief said that there were several factors that complicated the rescue effort following the tornado that went through the area.
"We had some concerns about safety of our workers because the building was still charged with electrical at that time. In addition to water that was leaking, the mains had broken, so water was pouring into the building. And then we also [had] gas leaking from natural gas," Whiteford said.
He said that emergency responders had to move "very slowly and methodically" to avoid more injuries. The first call to emergency responders was made at about 8:35 p.m. on Friday.
Whiteford also noted that the building collapsed in the middle of a shift change, and the number of people in the Amazon facility was fluctuating at the time. Because of that, he said a clear number of people inside the building at the time of the collapse could not be released.
According to Whiteford, the walls on both sides of the building collapsed inward, and the roof of the building collapsed downward.
"Most of the weight of the building landed centrally into the building, and its walls are made out of 11-inch thick concrete and there are about 40-feet tall. So a lot of weight when that came down," he said.
Pritzker added that he has spoken with people from Amazon and said that the company intends to assist the community in the recovery efforts.
"I also spoke with Amazon earlier today and implored them to provide every assistance to this community, which they have said they intend to do," Pritzker said.
The National Weather Service tweeted on Sunday that the tornado that the damage observed at the Amazon warehouse was equivalent to an EF-3 tornado. Top speeds from the tornado are estimated to be around 155 mph.
However, the government agency said the rating could increase as more damage is surveyed.
Fox News' Brie Stimson contributed to this report