Bloomington police chief Jeff Potts told reporters the police were called to the mall at 10:17 am local time, and initial information indicated that a third-level child inside the mall was being rushed to the mall first level had fallen.
Additional evidence from witnesses indicated that the 5-year-old may have been pushed or thrown, Potts said.
Police officers gave the child first aid along with witnesses, Potts said.
"The child has suffered significant injuries," he said. "The child was taken to a hospital and looked after."
According to Potts, police witnesses said that the person suspected of pushing or throwing the child "left immediately after the incident". The suspect, a 24-year-old man, was soon found in the mall and taken into custody.
He is currently in the Bloomington Police Department, Potts said, and the authorities do not believe there is another threat to the public.
"At this point, we do not believe there is a relationship between the child or the child's family," Potts said, stressing that the police considered this an "isolated incident".
The area in which the case occurred was closed.
"She screamed," Everyone is praying, everyone is praying. Oh my God, my baby, someone threw him over the edge, "Brian Johnson told WCCO.
A Mall of America spokesman said in a statement that additional information about the incident would come from the police.
Melissa Alonso of CNN contributed to this report.