Broadcast live on TV nationwide, the ceremony was held at the Rajapracha Samakhom Pavilion of Klai Kanwon Palace in the resort city of Hua Hin in Prachuap Khiri Khan Province.
The royal motorcade started to move slowly towards the pavilion at around 10:15 am local time. The king waved to tens of thousands of people who were waiting along the road and chanting " Long Live the King." Many of the well-wishers had been waiting since Sunday.
The ceremony was attended by members of the royal family, caretaker cabinet members and senior government officials, including caretaker Prime Minister Yingluck Shinawatra and Privy Council president Prem Tinsulanonda. It ended at about 11 am.
The 86-year-old king was crowned on May 5, 1950 at the Royal Palace in Bangkok.