The Thai Maritime Enforcement Command Centre Region 3 branch (Thai-MECC 3) was alerted to the man overboard at 4:10pm, with a report saying that a fishing boat with two people had overturned about halfway between Tha Sak Pier and Koh Ngam.
The boat had overturned about one kilometre from shore.
One man swam safely to shore, while the other reportedly clung to the boat for 20 minutes before disappearing.
Vice Admiral Suwat Donsakun, Director of Thai-MECC 3, ordered immediate coordination with the Phuket Marine Office and the Royal Thai Navy Third Naval Area Command to dispatch search teams. Local agencies also joined the effort.
However, despite extensive efforts, the missing person has not yet been located.
The search was paused at sunset yesterday and resumed at 8am today (June 24).
Authorities urge anyone with information or sightings in the area to contact the Thai-MECC 3 at hotline 1465, available 24 hours.