He said Thailand has been a peaceful country for a long time, with Thai people united and working to support each other for the national interest.
"All Thais should realise this point a lot and behave and perform our duties accordingly, our duty for the sake of the public, for stability, security for our nation of Thailand," His Majesty said, then expressed the wish that all Thai people should be happy.
Prior to his arrival at Rajpracha Samakhom Pavilion, many thousands of well-wishers wearing yellow shirts and waving yellow flags - the colour yellow symbolising the King - lined Phetkasem Road, the approach to the palace, eager for the opportunity to catch a glimpse of His Majesty on his short trip to the venue for the grand audience.
Many were noticeably emotional, and some were seen crying as His Majesty passed by to loud cheers and cries of "Long live the King!".
The royal procession was broadcast live on television nationwide, as was the grand audience.
He was received at the Rajpracha Samakhom Pavilion by members of the royal family, but there was no appearance by Her Majesty the Queen.
The military fired a 21-gun salute as the King made his appearance in the pavilion.
His Royal Highness Crown Prince Maha Vajiralongkorn, Prime Minister Yingluck Shinawatra and House Speaker and Parliament President Somsak Kiatsuranont each wished His Majesty a happy birthday.
HRH Crown Prince Maha Vajiralongkorn said Thai people were grateful to be living in Thailand during the reign of His Majesty. "We vow to behave well to follow the good example set by His Majesty," he said.
Prime Minister Yingluck Shinawatra said the King, out of kindness, initiated the first royal project at Khao Tao water reservoir in Hua Hin at the beginning of his reign. His kindness had been shining for a long time, she said. The Thai people wish the King to have no worries and to be filled with happiness.