Celebrations are taking place in Thailand to mark the 80th birthday of King Bhumibol Adulyadej, the world's longest serving monarch.
Thais revere King Bhumibol Adulyadej
Thousands of people packed the streets around Bangkok's Grand Palace to show their respect for the king, who is revered after 61 years on the throne.
The festivities come amid growing fears over King Bhumibol's fragile health.
Last month he spent three weeks in hospital being treated for inadequate blood flow to the brain.
The king's birthday is an occasion for celebration in Thailand, but also a time of acute anxiety, reports the BBC's Jonathan Head from Bangkok.
During his many years on the throne, public adulation for King Bhumibol has risen to such an intensity that few Thais can imagine how the country will cope without him.
Many have taken to wearing yellow or pink over the past year, colours associated with the king.
A stiff, unsmiling figure in public, he has steered a legally almost powerless monarchy through a succession of unstable military and civilian governments, and acquired an unrivalled aura of virtue and integrity, our correspondent says.
Huge crowds waited on the streets of the capital to watch the king's motorcade pass by on its way to the Grand Palace.
There, wearing a gold ceremonial robe, King Bhumibol delivered a short speech that was broadcast live across the nation.
Many Thais have been wearing the pink and yellow shirts
He reiterated the need for national unity, something he emphasised in a longer televised address on Tuesday.
Then he urged solidarity between the military and civilians, a veiled reference to the bitter divisions in Thailand over last year's coup which ousted Prime Minister Thaksin Shinawatra.
"Whether soldiers or civilians, (we) must be united, like our legs that must be united - which means one goes forward and one pushes back before moving forward," he said.
"This way, we could walk without falling. Without unity, the country will face disaster."
The country is due to return to democratic rule after a general election later this month.
Polling will take place on 23 December and many analysts believe that the most likely outcome will be a weak coalition government.
The monarch also strove to reassure people that his health was fine, despite the recent spell in hospital.
Fears over King Bhumibol's health have been heightened by uncertainties over the succession, our correspondent adds.
His son, Crown Prince Vajiralongkorn, has been groomed to succeed, but doubts are frequently expressed over his capabilities.
The Thai monarchy is protected by strict laws which ban any criticism of members of the royal family.