In a pre-recorded TV address, the crown prince has formally accepted parliament's invitation to become Rama X, the country's new monarch. King Vajiralongkorn succeeds his late father, who died in October.
Prince Vajiralongkorn granted an audience late on Thursday to Prime Minister Prayut Chan-ocha and other senior dignitaries for the official acceptance, which took place during a somber ceremony at the Dusit Palace royal residences in Bangkok.
"I hereby accept the invitation to become the new king in accordance with the wish of the King Bhumibol Adulyadej and for the benefit of all the Thai people," he said.
Buddhist temples across the country were asked to beat drums and gongs immediately after his proclamation, which was broadcast simultaneously by all Thai TV channels.
In acceding to the throne, he allays concerns by some Thais that the country was headed for a period of instability following the death on October 13 of his father, King Bhumibol, who reigned for 70 years.
Formal titles confirmed
The 64-year-old will be known as King Maha Vajiralongkorn Bodindradebayavarangkun, according to a statement released by parliament's public relations department.
He will also be known as Rama X, or the 10th king of Thailand's Chakri Dynasty.
A coronation will take place in a year's time, once his father has been cremated. Thai authorities are building a special site where Bhumibol's remains will be cremated.
Vajiralongkorn had requested more time to mourn his father's death, and instead of his immediate accession, the head of the king's advisory council, Prem Tinsulanonda, served temporarily as regent.
One of his first acts as monarch will be to endorse a new constitution drafted by the military.
Its acceptance will pave the way for an election in late 2017, the country's military junta has said, after it was overwhelmingly endorsed by the public in a referendum in August. The junta took power, promising swift elections, in 2014.
Big shoes to fill
The new monarch has yet to command the kind of adoration that his father received from Thais and he has kept a much lower profile throughout most of his adult life, having spent much of it abroad.
He has a home in southern Germany.
But as his father's health deteriorated in recent years, Vajiralongkorn took on more of the monarch's ceremonial duties.
King Bhumibol was widely loved and regarded as a pillar of stability during decades of political turbulence and rapid economic development.
Analysts said the king will be keen to maintain strong ties between the royal household and the military, which toppled an elected government in 2014. Thailand has had 19 military coups since the abolition of the absolute monarchy in 1932.
mm/msh (dpa, Reuters)