The nation has experienced its greatest sorrow in a lifetime on Oct 13 and will have a new king under its traditions, Prime Minister Prayut Chan-o-cha announced on Thursday evening.
The Thai people's greatest loss came after King Rama VIII passed away on June 9, 1946. The past 70 years of King Rama IX's reign have proved to be a period of great happiness, hope and benefit thanks to the ascension of King Rama IX who healed the people's despair after the end of World War II, Gen Prayut said.
"His Majesty the King brought people from their hopelessness to their determination, security and courage to cope with obstacles," the prime minister said.
"The reign was a period of comprehensive national development. His Majesty was the beloved King who was the spiritual centre of all Thai people. It was really a 70-year period of righteous reign for the benefit and happiness of Thai people."
In recent years, His Majesty the King had fallen sick. Royal doctors had treated the King attentively and during the King's periods of recovery, His Majesty managed to return to his work for the public interest, the prime minister said.
Finally the King's illness could not be alleviated and that led to his death, he said.
"October 13 will be in the memory of Thai people for good," Gen Prayut said. "It was a 70-year period of limitless public benefit and now it is limitless sorrow for the people."
He asked people to pray for the peaceful spirit of His Majesty the King in heaven, follow His Majesty's guidelines and join hands to sustain national prosperity and happiness as His Majesty wished.
Gen Prayut said the succession of the monarch would comply with the constitution, the royal law and royal tradition.
"The government will inform the National Legislative Assembly that His Majesty the King had appointed the heir in accordance with the royal law on December 28, 1972, and then the National Legislative Assembly will take the relevant action," he said.
The prime minister asked people to follow only official information from the government and ignore rumours without a source.
"Please take the opportunity to boost one another's morale. All of us share the same feelings because we have our common father of the nation. Please help protect national peace and do not let anyone trigger conflicts that would lead to turmoil," Gen Prayut said.
He also asked people to wear mourning clothes for a year. He said government offices will fly their flags at half-mast and that people should refrain from entertainment activities for 30 days.
"Thai people. His Majesty King Bhumibol Adulyadej, King Rama IX, has passed away. Long live the new king," the prime minister said in concluding his speech.
According to Section 23 of the 2007 constitution, when the throne becomes vacant and the king has already appointed his Heir under the 1924 Palace Law on Succession, the cabinet shall notify the Parliament president, who will convene members for acknowledgement.
The parliament president will then invite the Heir to ascend the throne and proclaim him King, according to the provision.
Since there is no Senate or House of Representatives at the moment, the 250-member National Legislative Assembly will act as parliament.
His Majesty King Bhumibol Adulyadej appointed His Royal Highness Prince Vajiralongkorn as the Heir to the Throne on Dec 28, 1972 after which he became His Royal Highness Crown Prince Maha Vajiralongkorn.
Although the 2007 charter was scrapped by the 2014 coup, the 2014 interim charter uses its chapter on the King as a reference.