Two men, aged 28 and 25, and a woman, aged 20, are being held at police stations across Hampshire. They are all from Southampton.
The unidentified body was found by firefighters after they were called to a blaze in a bin at the Empress Road industrial estate in the early hours of the morning.
Police said they were still appealing for information, particularly from anyone who may have witnessed suspicious activity in or around the industrial estate, off Thomas Lewis Way, overnight.
Detective Inspector Simon Baker, who is leading the murder hunt, said: "We are making urgent inquiries to identify the body."
He said he was unable to say whether the victim was male or female, their age or how badly burned the body was.
The area where the body was found is part of Southampton's red light district. Source
:: Witnesses are asked to contact police on 101, quoting Operation Waterloo, or call the Crimestoppers charity anonymously on 0800 555 111.