The rubbish collector was working his rounds in the Suksan area of Rawai about 1pm on Friday (June 14) when he found the black plastic trash bag containing the baby's body.
The collector and his colleagues immediately called the Chalong police station. When the police arrived they found that a length of rubber balloon had been tied around the baby's neck, and that it was probably dead before it was dumped.
Emergency workers from the Phuket Raujai Rescue Foundation who also attended the scene said they believed the baby was less than a day old.
The police took the body to Vachira Hospital for a post-mortem investigation, and say they're now looking for the mother of the dead child.