A statement from the royal household bureau said King Bhumibol Adulyadej, who was the world’s longest-reigning monarch, “passed away peacefully” at 3.52pm (8.52am BST) on Thursday at Siriraj hospital in Bangkok.

He took the throne of the kingdom shortly after World War II and held it for more than 70 years. Bhumibol Adulyadej, politically influential and highly revered, was a unifying figure in a deeply polarized country, and his death casts a pall of uncertainty across Thailand.

Thailand’s prime minister, Prayut Chan-ocha, dressed in a black suit, appeared on domestic television channels minutes after the announcement and confirmed that the Crown Prince Maha Vajiralongkorn will succeed to the throne. He said the nation will observe a year-long mourning period.

The constitutional monarch has been absent from public life for years and his death throws an already politically turbulent Thailand into a haze of uncertainty that is unprecedented in its modern history.

His constant presence has made Thailand one of the most widely cited development successes, becoming an upper-income country in less than a generation.

King Bhumibol Adulyadej has successfully negotiated many times with military leaders to return democracy to the country, but finally leaves Thailand to the army.

King Bhumibol had been treated by doctors for “water on the brain” and a chest infection in August 2015. On Sunday, the palace said his condition had become unstable.

His wife, Queen Sirikit, has also suffered declining health. They have three children, but their only son and heir, Crown Prince Maha Vajiralongkorn, does not command the same affection as his father, causing fears of a rupture in the state’s structure.