The raid occurred early Sunday at a rural property in Benton County, which is about 70 miles southeast of Memphis, The Commercial Appeal newspaper in Memphis reported.
A dogfight was in progress when authorities arrived and several people in the crowd of about 200 fired guns, a statement from the Humane Society said.
Chris Schindler, the society's manager of animal fighting investigations, was at the scene but said he was unsure how many people were arrested. Law enforcement officials hadn't commented on the raid.
"Something like this is going to send shock waves through the entire dogfighting community," Schindler said.
Schindler said of the 20 dogs seized at the scene, two showed signs of recently being fought previously.
"One dog is far worse off than the other dog," Schindler said. "Unfortunately in dog fighting, these dogs suffer a great deal of trauma, blood loss, shock."
All of the dogs are being cared for by the Humane Society, Schindler said.
The Humane Society has offered a $5,000 reward for information that leads to the arrest and conviction of any person involved in illegal animal fighting.