Millions of Thais across the country on Saturday (Dec 5) are celebrating the 88th birthday of King Bhumibol Adulyadej, the world's longest-reigning monarch, who has been king since 1946.
In temples and town halls, Thais have gathered to offer prayers for the King's health.
In Phichit province, police and locals donated blood for local hospitals; in Yala in the south more than 300 parents, teachers and students rode bicycles to a home for the elderly, taking food for the residents of the home. In the resort town of Krabi, locals gathered to clear beaches of garbage.
King Bhumibol is the only King most Thais alive today have ever known. He is widely revered, many even ascribing divine powers to him.
Considered an embodiment of Thailand's cultural identity, he has also been seen as a stabilising force in the fractious and often brutal world of Thai politics.
But there is also gathering 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 in September.
A few hundred gathered at the hospital on Saturday morning, dressed in yellow - the King's colour - hoping for a glimpse of him from his hospital room.
Many had come at dawn in the hope of seeing the King, or the Crown Prince or the royal princesses when they visited the hospital to greet him. Some had even camped in the grounds overnight.
But the mood was sombre, and word had gone around that he would not appear. Some were in tears as they sang the King's anthem at 9am, followed by prayers for his health.
Five young women - accountants, teachers and a real estate agent - said they were there for the fourth time running for his birthday.
They gazed up at the remorseless hospital block, each with a different theory on which room the King was in. They would stay all morning, they said, hoping for a glimpse of him or the other royals.
In the evening at the sprawling Sanam Luang grounds in old Bangkok, next to the Grand Palace, there will be festivities - lights and candles and music and fireworks.
But one of the young women at the hospital, 43 year old Amorn Thongsongson, told The Straits Times: "There will be many people at Sanam Luang, but we won't go. Our hearts are here, in hospital with him."