Crown Prince Maha Vajiralongkorn will be proclaimed the new king of Thailand late Thursday, his office said, opening a new chapter for the powerful monarchy in a country still mourning the death of his father.

   Vajiralongkorn, 64, who inherits one of the world's richest monarchies as well as a politically troubled nation, will ascend the throne 50 days after King Bhumibol Adulyadej's death.

   As dusk fell in Bangkok, the prince arrived at the Grand Palace where his father's body lies in state for religious rites to mark the 50th day since his death.

   In complex protocols, the prince will later grant an audience to grandees including the junta leader and the head of the National Legislative Assembly, who will invite Vajiralongkorn to become king.

   "The Crown Prince will deliver an acceptance speech... after that he will pay respects in front of a portrait of the king," the statement added.

   Buddhist temples across the country have been asked to beat drums and gongs after his proclamation.

   He will be named Rama X of Thailand's Chakri dynasty, but will not formally be crowned until after his father's cremation, which is expected next year.

   Bhumibol's reign, which ended on October 13, spanned seven turmoil-laden decades, pockmarked by a communist insurgency, coups and street protests.

   To many Thais Bhumibol was the only consistent force in a politically combustible country, his image burnished by ritual and shielded by a harsh royal defamation law.

   Vajiralongkorn, who has been named successor for more than four decades, does not yet enjoy the same level of popularity.

   He spends much of his time outside of the public eye, particularly in southern Germany where he owns property.

   He has had three high-profile divorces, while a recent police corruption scandal linked to the family of his previous wife allowed the public a rare glimpse of palace affairs.

   Thursday's ascension will end a period of uncertainty which followed a shock junta announcement after Bhumibol's death that the prince had asked to delay his official proclamation so he could mourn.

   Thailand's constitutional monarchy has limited formal powers.

   But it draws the loyalty of much of the kingdom's super-rich business elite as well as a military that dominates politics through its regular coups.

   It is also protected from criticism by one of the world's harshest lese majeste laws, carrying up to 15 years in jail for every charge of defaming the king, queen, heir or regent.

   That law makes open discussion about the royal family's role all but impossible inside the kingdom and means all media based inside the country routinely self-censor.

   Convictions for so-called "112" offences -- named after its criminal code
-- have skyrocketed since generals seized power in 2014.

   Experts say most have targeted the junta's political opponents, many of whom support the toppled civilian government of Yingluck Shinawatra. (AFP)