American Top Team, a facility where he trained in Coconut Creek, Florida, announced Slice's death on Twitter.
"The ATT Family and South Florida community lost a legend today. RIP KIMBO," their Tweet read.
Slice was taken from his home in Coral Gables, Florida to a hospital in Fort Lauderdale on Monday. Sergeant Carla Kmiotek of the Coral Springs police told Yahoo Sports: "We did not receive a police or EMS call from the residence.
"There is no foul play suspected and there is no investigation. It is being handled as a medical incident."
Scott Coker, president of Bellator MMA, an organisation for which Slice competed, said in a statement: "We are all shocked and saddened by the devastating and untimely loss of Kimbo Slice, a beloved member of the Bellator family.
"One of the most popular MMA fighters ever, Kimbo was a charismatic, larger-than-life personality that transcended the sport.
"Outside of the cage he was a friendly, gentle giant and a devoted family man."
Slice, who was born as Kevin Ferguson in Nassau, Bahamas, and attended the University of Miami and Bethune-Cook University, compiled a 5-2-1 career MMA record between the UFC and Bellator and was 7-0 with six knockouts in seven professional boxing fights.
He last fought at Bellator 149 in February, defeating Dhafir "Dada 5000" Harris. Slice later tested positive for steroids, wiping the victory from the record books.
(Editing by Peter Rutherford)
