BANGKOK: Thailand's new King Maha Vajiralongkorn has pardoned tens of thousands of prisoners, a first act of "mercy" as monarch as he reaches out to his subjects following the death of his beloved father.

Revered King Bhumibol Adulyadej died in October aged 88 after a seven-decade reign, leaving the politically febrile nation without its unifying figure.

His only son, 64-year-old Vajiralongkorn, was proclaimed king in early December.

But the thrice-divorced monarch is yet to draw the same level of devotion from a public well-versed in rumours over his private life even if any criticism of him is illegal.

The prisoner pardon was Vajiralongkorn's "first chance since he succeeded the throne to show the king's mercy", according to a statement published Sunday in palace mouthpiece the Royal Gazette.

Pardons were annual events under Bhumibol.

Women jailed for first offences, some inmates who have served one third of their sentences, and prisoners with disabilities or serious illness were among those pardoned.

The decree did not say how many prisoners will be freed.

However the Bangkok Post, quoting Corrections Department chief Kobkait Kasiwat, said as many as 30,000 qualified for release, with another 70,000 expected to have their sentences reduced.

Ritual, propaganda and law underpin the status of Thailand's monarchy.

Thai schoolchildren are taught the primacy of the institution, while huge portraits of key royals adorn virtually every main street.

Like his father, Vajiralongkorn is shielded from criticism by a harsh royal defamation law that carries up to 15 years in jail per charge.

That has forced a culture of self-censorship upon the media, academia and the arts.

The prisoner pardons follow a slew of public appearances by the new king, whose four decades as designated heir were characterised by publicity-shyness and long trips overseas.

Since he was proclaimed King Rama X, the new monarch has offered flood relief, opened a town hall and been honoured in a video tribute played in cinemas.