BANGKOK (AFP) - Thailand's revered but ailing King Bhumibol Adulyadej made a rare public appearance on Tuesday, leaving the hospital where he has been convalescing for much of the last few months.

A heavily guarded convoy carrying the wheelchair-bound 87-year-old monarch left Bangkok's Siriraj Hospital for the Grand Palace, the sprawling complex in the heart of the old quarter that is the seat of the Chakri dynasty.

The palace visit was made on Coronation Day, a Thai public holiday that marks King Bhumibol's official coronation in 1950, three years after his reign began following the death of his brother.

The appearance of the world's longest serving monarch after a recent no show will be a source of relief for many Thais who revere him as a semi-divine figure.

He had been expected to appear publicly for his birthday in December, a time when the monarch traditionally addresses his people. But the public audience was cancelled at the last minute on the advice of his doctors.

There is profound concern in Thailand over the kingdom's future as Bhumibol's reign enters its twilight years following nearly a decade of political turbulence.

King Bhumibol, formally known as Rama IX, has spent most of the last few months in hospital after undergoing an operation to remove his gall bladder in October.

In the last two months Bhumibol had made two brief trips from his hospital bed, one in early May to a nearby palace and one last month to view the Chao Praya river that runs through Bangkok.