More than 1,000 people gathered at Provincial Hall at 8am for the Phuket event, where Phuket Governor Chockchai Dejamornthan led officials and residents in the mass singing and oath-taking ceremony.
Standing in front of a portrait of the late HM King Bhumibol, the officials and residents pledged to do good for the kingdom, religion and the monarchy.
They also sang Royal Anthem and vowed to be loyal to every monarch of the Chakri Dynasty, which have ruled over Thailand in unbroken succession for more then 200 years.
In Patong, more than 500 people led by Patong Mayor Chalermluck Kebsup gathered at the courtyard next to Patong Municipality office for the event.
In Rawai, after the mass singing and oath-taking ceremony, Rawai Mayor Aroon Solos led officials, residents and students in a beach cleanup.