The longest-reigning monarch in the world, King Bhumibol Adulyadej of Thailand, turned 88 yesterday, in frail health but revered by his people after nearly 70 years on the throne.
In temples and town halls, millions of Thais gathered to offer prayers for the monarch's health, and "make merit" in his name.
In Phichit province, for instance, police and locals donated blood while residents in the resort town of Krabi gathered to clear beaches of garbage. In the southern province of Yala, more than 300 parents, teachers and students rode bicycles to a home for the elderly, with food for its residents.
At Bangkok's Siriraj Hospital, a few hundred people gathered in the morning, hoping for a rare glimpse of him in the window of his hospital room. But he did not appear. Several in the crowd were in tears as they sang the King's anthem. Later they chanted Buddhist prayers.
Advertising executive Sanpathit Tavijaroen, 39, and his wife Amie Chutimon Chanmuan, 30, who works for an international bank, have watched the King on television on his birthday since they were young, Mr Sanpathit said.
"We always wanted to come but were too busy; this time we made it," he said. "He's not a King who has just sat around. He has worked every day, and devoted himself to the people all his life."
King Bhumibol - who ascended the throne in 1946 - is the only monarch most Thais have ever known. He is considered an embodiment of Thailand's cultural identity, and has also been seen as a stabilising force in the fractious and often brutal world of politics in the kingdom.
Even though he is a constitutional monarch, King Bhumibol is a powerful force, as he is seen to be the highest moral authority in the land. The Constitution states that "the King shall be enthroned in a position of revered worship and shall not be violated".
But the role of the monarchy has been at the core of recent political unrest, and underlying the enthusiasm of the hundreds gathered at the hospital - and the many more who thronged the sprawling Sanam Luang grounds next to the Grand Palace in old Bangkok last night for a candlelight tribute and fireworks - is increasing anxiety at the prospect of a future without him.
The King is ailing, and has been living in Bangkok's Siriraj Hospital for most of the last six years. He was last seen in public on Sept 1.
"I wish he could live forever," said 81-year-old fruit seller Thanom Chompoo, who has been coming to the hospital twice or thrice a week since 2006. "I know he is old, but I will still be in shock if anything happens to him."
The army, which seized power in May last year, has made cracking down on people deemed critical of the monarchy one of its top priorities in King Bhumibol's twilight years, resorting frequently to the harsh law against lese majeste. Article 112 states that whoever defames, insults or threatens the King, queen, heir-apparent or regent, can be put in jail for up to 15 years.
The regime has made it explicit that any hint of dissent, particularly towards the monarchy, will not be tolerated. Recent sentences have been harsh; in August, military courts handed down record 28-year and 30-year sentences to two people charged with posting content on Facebook deemed insulting to the monarchy.
Only in recent weeks, 10 people, including senior police and military officers, have been charged with a range of offences, including corruption and alleged royal defamation, over their involvement in two nationwide cycling events led by the Crown Prince Maha Vajiralongkorn - his first major, mass public events. Two of the suspects died in military custody.