Lt Sopanat Nayao of the Thalang Police was called to the scene, in Soi Taphang in Moo 4, Thepkrasattri, at 5:30am.
Sasikan Chuaychu, 32, from Yantakao, Trang, told police that she was sleeping when she was woken by the sound of a baby crying.
She opened her front door to find the baby boy swaddled in a cloth on her doorstep.
Beside the baby was a plastic bag containing a milk bottle and diapers.
Where the umbilical cord had been severed was still a raw wound, and rescue workers soon at the scene rushed the baby to Thalang Hospital for care.
Lt Sopanat said police are continuing their investigation, including checking CCTV in the area, in the hope of identifying and contacting the mother or other relatives of the baby boy.