The world's longest-reigning monarch, Thailand's King Bhumibol Adulyadej, died in hospital on Thursday (Oct 13), the palace said in an announcement. He was 88.
"His Majesty has passed away at Siriraj Hospital peacefully," the palace said, adding that he died at 3.52pm Bangkok time (4.52pm Singapore time).
Prime Minister Prayut Chan-o-cha, in a televised address on Thursday evening, declared that mourning will last for one year, and flags will fly at half mast for 30 days. There will be no entertainment for 30 days too.
He said an heir to throne has been designated since 1972 and the cabinet will inform Parliament. He also urged Thais to love one another and protect "the father's land."
A specially convened Parliament meeting was held late on Thursday, which commenced after a nine-minute silence to mark the death of King Bhumibol
King Bhumibol, whose name means "Strength of the Land", was seen as a father figure in the country of 68 million. Formally known as Rama IX of the Chakri Dynasty, he was the last king to yield real power in a region where old, once-powerful monarchies - in Myanmar, Laos, Vietnam and Cambodia - had long disappeared.
Thailand now moves into unknown territory but in the short term, with the royalist army firmly in power, there may be a period of stability, analysts say.
While absolute monarchy in Thailand was abolished in 1932, the institution remained a potent symbol and King Bhumibol, who was plunged into the role at age 18, rebuilt the reputation and moral authority of the monarchy to probably its peak.
His image - assiduously cultivated by the state with layers of ritual, ceremony and protocol -was that of a Dhammaraja or righteous king, impassively above the political fray. While on paper Thailand is a constitutional monarchy, in reality King Bhumibol was the kingdom's highest moral authority.
He was only 18 years old when he had to agree to become king, descending into a world of cut throat political intrigue following the sudden death of his brother King Ananda Mahidol from a gunshot in his own bed in 1946.
With 70 years on the throne, King Bhumibol is the only king the vast majority of Thais have ever known.
The wide respect and reverence for him was largely due to state-sponsored ceremony and ritual, and the harsh lese majeste law which stifles critical debate on the royal family's role - an issue increasingly underlying the political conflict of the last decade.
But the king also earned his popularity by travelling seemingly indefatigably throughout the country, especially in his younger days on the throne, speaking with people from all walks of life and starting thousands of projects to help the poor and marginalised.
In the 1970s, an active and benevolent monarchy also proved to be a bulwark against communism. Thailand became an ally of the United States in 1833 with a Treaty of Amity and Cooperation, and the fight against communism cemented the alliance when US and Thai troops fought side by side in the Korean and Vietnam wars. In the 1960s and 1970s, communist insurgents in Thailand, seeking to overthrow the monarchy, fought government troops as well. The king's pro-poor projects in the impoverished north and north-east, and his benevolent ''people's King'' image, helped blunt communist propaganda.
Under King Bhumibol, Thailand has grown from an essentially agricultural population surrounded by turmoil and war and beset with local insurgencies, to a middle-income country of 68 million with thriving export and tourism sectors, resilient enough to bounce back from crises like the Asian financial crash of 1997.
Bangkok, a once swampy low-rise capital, outstripped its neighbours to transform into a gleaming modern city and the hub of mainland South-east Asia.
A keen musician and yachtsman in his youth, King Bhumibol's interest in science led him to focus particularly on water management and irrigation projects. He patented a water wheel and a cloud-seeding rainmaking method - once demonstrating it for visiting Singaporean officials.
King Bhumibol wielded his moral authority sparingly, taking care to stay above the political fray. In a rare interview in 1974, he said he found politics a "filthy business''.
But his authority was underscored in 1992 when thousands of pro-democracy protesters challenged military dictator Suchinda Kraprayoon, who responded with a ruthless armed crackdown. As smoke from burning buildings billowed above Bangkok, the king summoned General Suchinda and his rival, retired general Chamlong Srimuang, who was leading the pro-democracy crowds.
The two rival leaders knelt before King Bhumibol as he lectured them, telling them - on television - that there would only be losers from the fight.
The intervention was a breath of relief in a harsh and conflicted atmosphere, and put huge moral pressure on the protagonists to step back, which they did, and the Suchinda government did not last.
King Bhumibol's passing is a watershed for a country racked over the last decade by political turmoil pitting royalist elites allied with the military principally against the network of the populist former prime minister Thaksin Shinawatra.
The struggle has seen two coups d'etat by the army in the name of protecting the monarchy against Mr Thaksin's network, in 2006 and in May 2014.
King Bhumibol had been the only real constant through Thailand's political ups and downs.
His picture - sometimes with his dog sitting alongside him - hangs in almost every Thai household and establishment like that of an elderly family patriarch.
Singapore conveyed its condolences to Thailand on Thursday (Oct 13).
"The Government of the Republic of Singapore is deeply saddened to learn of the passing of His Majesty King Bhumibol Adulyadej of the Kingdom of Thailand," the Ministry of Foreign Affairs (MFA) said in a statement.