Thailand's ailing King Bhumibol Adulyadej has cancelled plans to hold an annual audience to mark his birthday on the advice of his doctors.

The king, who turned 87 on Friday, has been hospitalised since early October when he had his gall bladder removed.

The cancellation, announced by the palace, will put a damper on public birthday celebrations, but will not come as a shock to most people.

However, the king's absence comes at a time of particular concern over his succession.

Next in line is Crown Prince Vajiralongkorn. In recent weeks, members of the family of his wife, Princess Srirasm, have been arrested on charges of abusing their connections for financial benefit.

The king last failed to make an appearance in 2008 for his 81st birthday celebrations following ill health.

A large crowd of well-wishers, many dressed in yellow and waving flags, gathered in the grounds of Bangkok's Siriraj Hospital where Thailand's monarch is admitted, according to the AFP news agency.

Anxious for the future

Most Thais have only known King Bhumibol on the throne and anxiety over the future once his six-decade reign ends is seen as an aggravating factor in Thailand's bitter political divide.

His period as a constitutional monarch has been pock-marked by nearly 20 attempted or successful coups, the last in May which saw the army topple the elected government.

Thailand remains under martial law, a condition the arch-royalist army said is necessary to keep the peace as it vows to expunge the kingdom of corruption and reboot Thai democracy.

Critics of the military said it has used its status as the defender of the monarchy as a pretext to grab power from the elected government aligned with Thaksin Shinawatra.

Thaksin's sister Yingluck was also forced out as prime minister shortly before the military's May takeover.

Thailand's monarchy is protected by one of the world's strictest laws and the army have ramped up prosecutions under the controversial legislation.

Both local and international media must heavily self-censor when covering the country's royal family.

Source: Agencies