Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, has died after 70 years as head of state, the palace says.
The 88-year-old king was widely revered but had been in poor health in recent years, making few public appearances.
He was seen as a stabilising figure in a country hit by cycles of political turmoil and multiple coups.
Crown Prince Maha Vajiralongkorn will be the new monarch, the prime minister has said.
The king's death means that Queen Elizabeth II is now the world's longest-reigning monarch.
Thailand's King Bhumibol Adulyadej dead at 88
BBC News
13 October 2016
King Bhumibol Adulyadej: 5 December 1927 - 13 October 2016
Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, has died after 70 years as head of state, the palace says.
The 88-year-old king was widely revered but had been in poor health in recent years, making few public appearances.
He was seen as a stabilising figure in a country hit by cycles of political turmoil and multiple coups.
Crown Prince Maha Vajiralongkorn will be the new monarch, the prime minister has said.
In a televised address to the nation, Prayut Chan-ocha said Thailand would hold a one-year mourning period and that all entertainment functions must be "toned down" for a month.
Describing the king's death as "the most devastating moment for Thais", the prime minister said: "He is now in heaven and may be looking over Thai citizens from there."
In a later statement he urged vigilance, saying national security was a top priority.
"Everyone will need to be alert in every region and throughout the country to ensure safety", the Reuters agency reported him as saying.
The king's death comes as Thailand remains under military rule following a coup in 2014.
King Bhumibol was widely respected across Thailand, and thought of by many as semi-divine.
Hundreds of mourners have gathered outside the Bangkok hospital where he died, stricken with grief at the news.
Crowds outside the hospital howled with grief when the announcement was made
Thai well-wishers mourn for Thai King Bhumibol Adulyadej after the announcement of his death at the Siriraj Hospital in Bangkok, Thailand, 13 October 2016
Many Thais worship the king with a near-religious fervour
Many held pictures of the king and wore yellow or pink clothing in his honour.
"How will Thailand live without you father?" cried one distressed man.
"I lost one of the most important people in my life. I feel like I haven't done enough for him," said another.
A palace official, speaking to crowds outside the hospital, said the body of the king would be moved to the Temple of the Emerald Buddha in Bangkok on Friday.
"His majesty has passed away at Siriraj Hospital peacefully," the palace statement said earlier, adding he had died at 15:52 (08:52 GMT).
Parliament is to hold a special session at 21:00 local time (14:00 GMT).
Crown Prince Vajiralongkorn, who is 64, is much less well known to Thais and has not attained his father's widespread popularity. He spends much of his time overseas, especially in Germany.
Strict lese-majeste laws mean public discussion of the succession are punishable by lengthy jail terms.
Given the pivotal role the king has played in maintaining the balance of power in Thailand's volatile political environment, the succession will be a formidable challenge for the government, says the BBC's Jonathan Head in Bangkok.
The Royal family tree
King Bhumibol, who was born in Cambridge in the US state of Massachusetts, acceded to the throne on 9 June 1946 after his brother, King Ananda Mahidol, died.
Though a constitutional monarch with limited powers, many Thais looked to King Bhumibol to intervene in times of high tension. He was seen as a unifying and calming influence through numerous coups and 20 constitutions.
However, his critics argued he had endorsed military takeovers and at times had failed to speak out against human rights abuses.
Following the death of King Bhumibol, Britain's Queen Elizabeth II has become the world longest-reigning monarch, having been on the throne for 64 years.
The world's longest-reigning monarchs: The world's longest-reigning monarchs - BBC News
Tributes have been flowing in from across the world.
US President Barack Obama called the late king a "tireless champion of his country's development".
"I had the honour of calling on his majesty the king during my visit to Thailand in 2012, and recall his grace and warmth, as well as his deep affection and compassion for the Thai people," he said.
UN Secretary General Ban Ki-Moon said in a statement that he hoped Thailand would honour King Bhumibol's legacy of commitment to universal values and respect for human rights.
A wave of emotion swept through the crowd - Jonah Fisher, BBC News, Bangkok
Throughout the first part of the day the king's supporters had sung royal songs and recited prayers at Siriraj Hospital. Many wore carefully chosen colours. Pink, for good health, or yellow, the royal colour.
Most knelt holding pictures of King Bhumibol, facing the part of the hospital where he had been receiving treatment.
By early afternoon the mood had begun to change. With all of his children at his bedside, rumours were circulating that the 88-year-old had passed away.
The tears began to flow, and in between songs the call of "God Save the King" was shouted with an almost visceral desperation.
Then just before 19:00 the news was official. A wave of emotion swept through the crowd. Many clung to each other and wept.
Thailand's father figure, a beacon of stability in a divided and worried country, had died. A new, more uncertain era has begun.
Thailand's King Bhumibol Adulyadej dead at 88 - BBC News
The 88-year-old king was widely revered but had been in poor health in recent years, making few public appearances.
He was seen as a stabilising figure in a country hit by cycles of political turmoil and multiple coups.
Crown Prince Maha Vajiralongkorn will be the new monarch, the prime minister has said.
The king's death means that Queen Elizabeth II is now the world's longest-reigning monarch.
Thailand's King Bhumibol Adulyadej dead at 88
BBC News
13 October 2016
King Bhumibol Adulyadej: 5 December 1927 - 13 October 2016
Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, has died after 70 years as head of state, the palace says.
The 88-year-old king was widely revered but had been in poor health in recent years, making few public appearances.
He was seen as a stabilising figure in a country hit by cycles of political turmoil and multiple coups.
Crown Prince Maha Vajiralongkorn will be the new monarch, the prime minister has said.
In a televised address to the nation, Prayut Chan-ocha said Thailand would hold a one-year mourning period and that all entertainment functions must be "toned down" for a month.
Describing the king's death as "the most devastating moment for Thais", the prime minister said: "He is now in heaven and may be looking over Thai citizens from there."
In a later statement he urged vigilance, saying national security was a top priority.
"Everyone will need to be alert in every region and throughout the country to ensure safety", the Reuters agency reported him as saying.
The king's death comes as Thailand remains under military rule following a coup in 2014.
King Bhumibol was widely respected across Thailand, and thought of by many as semi-divine.
Hundreds of mourners have gathered outside the Bangkok hospital where he died, stricken with grief at the news.
Crowds outside the hospital howled with grief when the announcement was made
Thai well-wishers mourn for Thai King Bhumibol Adulyadej after the announcement of his death at the Siriraj Hospital in Bangkok, Thailand, 13 October 2016
Many Thais worship the king with a near-religious fervour
Many held pictures of the king and wore yellow or pink clothing in his honour.
"How will Thailand live without you father?" cried one distressed man.
"I lost one of the most important people in my life. I feel like I haven't done enough for him," said another.
A palace official, speaking to crowds outside the hospital, said the body of the king would be moved to the Temple of the Emerald Buddha in Bangkok on Friday.
"His majesty has passed away at Siriraj Hospital peacefully," the palace statement said earlier, adding he had died at 15:52 (08:52 GMT).
Parliament is to hold a special session at 21:00 local time (14:00 GMT).
Crown Prince Vajiralongkorn, who is 64, is much less well known to Thais and has not attained his father's widespread popularity. He spends much of his time overseas, especially in Germany.
Strict lese-majeste laws mean public discussion of the succession are punishable by lengthy jail terms.
Given the pivotal role the king has played in maintaining the balance of power in Thailand's volatile political environment, the succession will be a formidable challenge for the government, says the BBC's Jonathan Head in Bangkok.
The Royal family tree
King Bhumibol, who was born in Cambridge in the US state of Massachusetts, acceded to the throne on 9 June 1946 after his brother, King Ananda Mahidol, died.
Though a constitutional monarch with limited powers, many Thais looked to King Bhumibol to intervene in times of high tension. He was seen as a unifying and calming influence through numerous coups and 20 constitutions.
However, his critics argued he had endorsed military takeovers and at times had failed to speak out against human rights abuses.
Following the death of King Bhumibol, Britain's Queen Elizabeth II has become the world longest-reigning monarch, having been on the throne for 64 years.
The world's longest-reigning monarchs: The world's longest-reigning monarchs - BBC News
Tributes have been flowing in from across the world.
US President Barack Obama called the late king a "tireless champion of his country's development".
"I had the honour of calling on his majesty the king during my visit to Thailand in 2012, and recall his grace and warmth, as well as his deep affection and compassion for the Thai people," he said.
UN Secretary General Ban Ki-Moon said in a statement that he hoped Thailand would honour King Bhumibol's legacy of commitment to universal values and respect for human rights.
A wave of emotion swept through the crowd - Jonah Fisher, BBC News, Bangkok
Throughout the first part of the day the king's supporters had sung royal songs and recited prayers at Siriraj Hospital. Many wore carefully chosen colours. Pink, for good health, or yellow, the royal colour.
Most knelt holding pictures of King Bhumibol, facing the part of the hospital where he had been receiving treatment.
By early afternoon the mood had begun to change. With all of his children at his bedside, rumours were circulating that the 88-year-old had passed away.
The tears began to flow, and in between songs the call of "God Save the King" was shouted with an almost visceral desperation.
Then just before 19:00 the news was official. A wave of emotion swept through the crowd. Many clung to each other and wept.
Thailand's father figure, a beacon of stability in a divided and worried country, had died. A new, more uncertain era has begun.
Thailand's King Bhumibol Adulyadej dead at 88 - BBC News
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