His Royal Highness Crown Prince Maha Vajiralongkorn presided over the ceremony to commemorate the 63rd anniversary of Coronation Day of His Majesty the King on Sunday at the Amarin Winitchai Throne Hall.
Her Majesty the Queen did not attend the ceremony.
The ceremony was attended by Her Royal Highness Princess Maha Chakri Sirindhorn and the crown prince's consort, Her Royal Highness Princess Srirasmi.
Earlier Sunday, the Royal Household Bureau said a team of royal physicians had advised His Majesty to suspend royal activities for a while.
The announcement said the result of an x-ray revealed that the inflammation in the King's lungs, diagnosed on April 28, had reduced. His Majesty was able to sleep but could not yet take much food and is tired, the bulletin said.