The search for survivors at an Amazon plant in Illinois where at least six workers were killed in a tornado was likely to take several days, but authorities said they did not anticipate finding any additional survivors.

Amazon has not specified how many people were inside the building when the tornado struck at 8:35 p.m. Friday, part of a swarm of hurricanes that destroyed entire villages across the Midwest and South.

Authorities stated that they did not have an accurate count of employees because it was a shift change and numerous part-time employees were present.

Some 45 individuals escaped the structure, with one being taken to a regional hospital for treatment, Edwardsville Fire Chief James Whiteford said during a Saturday evening news conference.

Amazon Worldwide Consumer chief executive officer Dave Clark expressed sadness for the deaths at the site and elsewhere.

"Our hearts go out to the victims, their families, and everyone who has been impacted by the storm's journey across the United States. We continue to provide assistance to our employees and partners in the area and throughout the storm-affected towns," Clark said in a tweet.

During a Monday morning press conference, police chief Mike Fillback told reporters that officials have had difficulty determining how many persons "we actually had at that facility at the time" because the institution does not have a defined staff.

Amazon management was on hand to assist in compiling a list of accounted-for staff members; nevertheless, Fillback cautions that it is still unclear how many people are trapped inside the fallen structure.

Although the exact number of persons in the building remains unknown, investigators think that up to 110 workers were inside at the time, according to NBC News.

According to Edwardsville Fire Chief James Whiteford, both sides of the warehouse used to prepare orders for delivery collapsed inward and the roof caved in.

Authorities received reports of trapped workers within six minutes, Whiteford said. Police assisted in rescuing victims from the rubble. While 45 colleagues escaped unharmed, six died and a seventh was evacuated to a hospital.

Illinois was not the only state to be impacted by severe weather. According to NBC News, 70 people are predicted to have died in Kentucky, while one person was killed in Arkansas after a potential tornado struck a nursing facility.

President Joe Biden of the United States tweeted Saturday morning that the administration is "working with local officials to ensure they have the resources they require while the search for survivors and damage assessments continue."